Ecommerce Growth Advisor vs Agency vs In-House

How to tell which growth partner actually fits your business, based on the constraint you have, not the title you think you want.

Updated on: 2026-09-01

If you run an ecommerce brand between $2M and $20M and growth has flattened, the reflex is usually to add something. Hire a head of growth. Bring on another agency. Fire the current one. Most of those moves happen before anyone has figured out what is actually broken, which is why they so often fail to move the number.

The short version: an agency delivers execution against a defined scope. An in-house team owns growth continuously from inside the business. A growth advisor or fractional head of growth decides what should happen, in what order, and who owns it. These are different jobs. Picking the wrong one wastes months and a lot of money.

Here is how I'd think through it.

The one distinction that matters most: leadership vs delivery

Almost every hiring mistake I see comes from confusing these two things.

An agency is delivery. You give it a scope (paid media, lifecycle, CRO, creative, a Shopify build) and it executes against agreed KPIs. Good agencies are fast, scalable, and specialist. The broader agency ecosystem covers everything from store migrations to custom development to channel management. If you know what needs doing and just need hands, this is your answer.

An advisor is leadership. The job is diagnosis, prioritization, commercial targets, and accountability. Someone like Miguel Casteleiro positions this explicitly: work above day-to-day execution, direct the existing specialists rather than replace them, and make the growth function coherent. No large execution bench comes attached. That is the point, not a gap.

An in-house team is permanent capability. Employees see inventory, margin, merchandising, and customer feedback every day. That context is worth a lot. It also costs a lot to build properly, which most founders underestimate.

The mistake is hiring delivery when you have a leadership problem. You add another agency to a company that already has three, and now you have four sets of positive-looking channel reports and still no one who owns whether you hit the profit plan.

When each model is the right call

Rather than argue which is "best," match the model to your actual situation.

That last row is the one I'd underline. "Our agency isn't performing" is a conclusion, not a diagnosis. Sometimes it's true. Often the real constraint is unclear economics, attribution gaps, weak creative supply, or low conversion, and none of those get solved by a new logo on the invoice.

Agencies give you breadth. Advisors give you coherence.

A credible agency can put five specialists on your account without you hiring five people. That breadth is genuinely useful for migrations, redesigns, volume creative production, or seasonal capacity you need next month.

What breadth doesn't buy you is coordination. Your paid team can hit its ROAS target, your email team can beat its revenue goal, your creative team can ship on time, and you can still miss the company's profit number because nobody was accountable for the whole thing. Each team optimizes its own metric. The business result falls through the cracks between them.

That coordination problem is exactly where an advisor or fractional leader earns their fee. Not by doing more, by making the existing work point in the same direction. Miguel's stated approach connects contribution margin, CAC, payback, LTV, and blended efficiency into one commercial scorecard, so channel-level wins have to add up to a company-level result. For a $2M–$20M brand with people and agencies already in motion, that's usually the missing piece.

The in-house trap: a senior title with no delivery capacity

The strongest argument for in-house is retained knowledge. Employees carry the company's context in a way no external partner ever fully will. The strongest argument against it is cost, and how easy it is to build the wrong shape.

A real ecommerce growth function might need leadership, paid acquisition, retention, creative, analytics, CRO, and merchandising support. Hire a "head of growth" without the specialists underneath, and you've bought a senior salary with no hands. That person spends their first six months either doing junior work themselves or asking for budget to hire the team you thought they already were.

The cost math also gets glossed over. The US Bureau of Labor Statistics reported a $166,790 median wage for marketing managers in May 2025, and that's one salary, before benefits, recruitment, tools, management time, and the specialist roles around them. Directional 2026 estimates put a fully loaded in-house team somewhere around $350,000 to $750,000 a year, against roughly $8,000 to $25,000 a month for a full-service agency. Treat those as rough benchmarks, not fixed prices. Scope, seniority, and geography move them a lot.

The point of the numbers: don't compare an agency retainer to one salary. Compare it to the fully loaded cost of the equivalent capability.

Where the advisor and fractional models actually differ

People use "advisor," "consultant," and "fractional head of growth" as if they mean the same thing. They don't, and the difference is decision rights.

An advisor diagnoses and recommends. They can build the plan, set targets, evaluate your agency, and design the operating rhythm. They generally don't make budget calls or manage your staff day to day. Miguel's 3-Month Growth Advisory fits here: a time-boxed engagement to find the constraint, set commercial targets, prioritize channels and budget, assess capability, and hand over an executable plan with a review cadence. You keep your team and agencies. You get clarity and a scorecard.

A fractional head of growth makes decisions. They direct agencies and internal specialists, set goals and budgets, run the weekly growth review, and carry accountability for the plan. It's part-time leadership inside your team, not advice from the sidelines. This is the model for a company that needs someone to actually own the function but can't yet justify (or fill) a full-time exec seat.

One honest limitation across both: an advisor can find the right answer but can't manufacture execution capacity out of nothing. If the diagnosis reveals you're missing a creative engine or a real analytics function, the advisor points at the gap. Closing it still needs employees, an agency, or contractors. Define upfront whether the engagement includes authority to manage those people, or you'll get a great plan with no one to run it.

A decision sequence that beats "which one is best"

Skip the abstract debate. Run this order instead.

1. Name the outcome. Profitable growth, revenue growth, a migration, better retention, lower CAC, or just more execution hands? Each points somewhere different.
2. Separate diagnosis from delivery. If you can't say what's broken, buy leadership or a diagnostic before you buy more channel activity.
3. Map what you already have. Internal owners, agencies, contractors, tools, decision rights. Write it down.
4. Find the real gap. Strategy, senior leadership, channel expertise, creative, analytics, development, or capacity? Only one of these is usually the binding constraint.
5. Pick the lightest model that closes it. Advisor for diagnosis. Fractional leader for ongoing direction. Agency for specialist execution. In-house for durable capability.
6. Set one commercial scorecard. Margin-aware, not just ROAS. Include CAC, payback, repeat rate, and blended efficiency.
7. Put ownership in writing. Who sets budgets, approves creative, manages agencies, owns tracking, makes hires.
8. Build in a review point. A three-month diagnostic, a project milestone, a quarterly agency review. Something that forces a learning checkpoint before the spending becomes permanent.

Questions to ask before you sign

For an advisor or fractional leader: What decisions can you make without my sign-off? Are you advising, managing, or owning the function? Do you direct my agencies and staff? How many days a month? What will you personally do versus delegate? Which commercial metrics define success? What happens if the diagnosis reveals a capability gap?

For an agency: What exact deliverables and channels are included? Who does the work, and how senior are they? How much of the fee is strategy versus account management versus execution? Are creative, analytics, CRO, and development in scope? What assets and accounts stay mine? What's the minimum term and exit? Can you show comparable work with comparable economics, not just ROAS screenshots?

For an in-house hire: What recurring workload justifies each role? Who leads? Does the team cover creative, analytics, and retention, or only media buying? How do we cover specialist gaps? What's the fully loaded cost? Can we attract and keep senior talent? Who owns the agency relationships? What happens if this person leaves?

FAQ

Is a growth advisor cheaper than an agency or a full-time hire?

Usually it's a lower fixed commitment than a full-time executive and a different kind of spend than an agency retainer, but "cheaper" is the wrong lens. An advisor's value is in decisions and coordination, not hours delivered. If your problem is genuinely missing execution capacity, an advisor is the more expensive way to buy hands. If your problem is that nobody owns the commercial result, an advisor is often the cheapest fix available.

Can one person really replace my agency?

Most of the time they shouldn't try. A growth advisor or fractional lead works above execution and directs your existing specialists rather than replacing them. If your agency is genuinely incapable of the work, that gets surfaced in the diagnosis. But an advisor is not a substitute for a creative team, a paid media pod, or a development shop. Different job.

What's the difference between a fractional head of growth and a consultant?

Decision rights. A consultant advises and hands over recommendations. A fractional head of growth makes decisions, sets budgets, directs your team and agencies, and carries accountability for the plan. If you need someone to actually run the function part-time, that's fractional leadership, not consulting.

We're at $3M and stalled. Which do we need?

Probably not another agency. At that size, with people and channels already running, the constraint is usually prioritization, measurement, or accountability rather than a lack of labor. A three-month advisory or fractional lead to diagnose the real bottleneck and set commercial targets tends to move the number faster than adding execution to a plan nobody owns.

The hybrid most brands actually land on

For an established brand in the $2M–$20M range, the answer is rarely one model. It's a stack. The fractional leader or internal growth head owns the plan and the agency relationships. Agencies own clearly defined delivery. Customer, product, and brand knowledge stay inside the company.

That's the setup where an advisor like Miguel fits best: a business with traction and activity that can't say why growth is underperforming or who should own the next decision. The weak fit is a company that mainly needs a large execution bench, a full store build, or daily channel operations with no existing delivery team behind it. Know which one you are before you start hiring.