Case studies are the primary sales tool for ecommerce marketing companies. They’re designed to build trust and demonstrate capability. The problem is that they’re also incredibly easy to manipulate.
Revenue numbers without context, ROAS figures from favourable attribution windows, and growth percentages that conveniently ignore what was happening before the agency took over. If you’re evaluating agencies and relying on case studies to make your decision, you need to know what to look for, what to question, and what should make you walk away.
Why Most Agency Case Studies Are Misleading (Even When They’re Technically True)
A Forrester survey found that nearly 70% of clients distrust marketing claims, citing inflated or fabricated case studies as a leading concern. That’s a striking number, and it reflects a real pattern in the agency world. The issue isn’t always outright fabrication. More often, it’s selective presentation.
An agency might show you a case study that reads: “We scaled this brand from £200,000 to £800,000 per month in revenue within 6 months.” That sounds impressive. But consider the questions it doesn’t answer:
What was the ad spend required to hit that revenue number? If they spent £400,000 to generate £800,000, that’s a 2x ROAS, which might be unprofitable depending on the brand’s margins.
Was the revenue growth profitable? Revenue is not profit. A brand can quadruple its revenue and still lose money if the cost of acquiring each customer exceeds the margin on each order.
What was happening before the agency took over? If the brand was already on a growth trajectory, the agency might be taking credit for momentum they inherited rather than created.
What attribution model are they using? Meta’s default 7-day click, 1-day view attribution window is generous. Numbers reported under that window will always look better than what Shopify actually shows in revenue received.
The Five Most Common Case Study Tricks
1. Revenue Without Spend Context
This is the most frequent issue. An agency shows impressive revenue figures but never mentions how much was spent to achieve them. A case study claiming “£1.2M in revenue generated” means nothing without knowing the ad spend, the agency fee, and the brand’s gross margin. Revenue is the top line. Profitability is what pays salaries and funds growth.
When you see revenue-only case studies, ask the agency directly: “What was the ad spend, and what was the client’s blended MER across all channels?” If they can’t or won’t answer, that’s your signal.
2. Cherry-Picked Timeframes
Agencies will naturally showcase their best months. A case study might highlight a Black Friday to Christmas period where every ecommerce brand sees a revenue spike, attributing seasonal performance to their strategy. Or they’ll show a 3-month window that captures the initial optimisation gains after taking over a poorly managed account, which makes any competent agency look brilliant.
The fix: ask for performance data across a full 12-month period, including the slow months. How an agency performs in January and February tells you far more than how they perform during peak season.
3. Platform-Reported Metrics Presented as Reality
Meta Ads Manager routinely over-reports conversions. Google Ads claims credit for purchases that would have happened organically. When an agency case study quotes “8x ROAS on Meta,” that’s the platform’s self-reported number. The actual contribution of those ads to real revenue is almost certainly lower.
Sophisticated ecommerce marketing companies will present case study data using blended metrics: total revenue divided by total ad spend across all channels, cross-referenced with Shopify data. If a case study only shows platform-reported numbers, the agency either doesn’t understand attribution or is choosing the most flattering angle.
4. Growth Percentages Without Baselines
“We grew this brand by 300%.” From what? If a brand was doing £10,000 per month and grew to £40,000, that’s 300% growth, but it’s a completely different achievement than growing a brand from £500,000 to £2M per month. Percentage claims without baselines are designed to sound impressive while hiding scale.
Always ask for the actual numbers behind the percentages. A 50% growth rate on a £2M per month brand is significantly harder to achieve, and far more relevant to your situation, than a 300% increase on a brand that was barely spending.
5. Anonymous Case Studies with No Verifiable Details
“A leading DTC skincare brand” or “a fast-growing fashion retailer” with no name, no website, no way to verify the claims. While some brands genuinely require confidentiality, an agency that has only anonymous case studies is giving you no way to check their work. The best agencies will have at least some named clients willing to speak to prospective customers.
How to Actually Verify Agency Claims
Ask to Speak to Current Clients
Not former clients. Not testimonial quotes on the website. Actual current clients you can call or video chat with. Prepare specific questions: How does the agency handle bad months? Have they ever recommended reducing spend? How responsive are they when things go wrong? Would you hire them again?
An agency that won’t connect you with current clients is either hiding dissatisfied customers or doesn’t have long-standing relationships, both of which are concerning.
Request a Live Account Walkthrough
Instead of relying on polished case study PDFs, ask the agency to walk you through an active campaign. They’ll need to anonymise certain details, but a live walkthrough reveals their actual working process: how campaigns are structured, how creative is organised, what testing is in progress, and how they make optimisation decisions.
This is hard to fake. An agency that can confidently walk you through a real account is demonstrating competence in real time, which is far more reliable than a designed presentation.
Look for Consistency Across Claims
If an agency claims to specialise in scaling brands from £50K to £500K per month in ad spend, their client list should reflect that. If their case studies are all small brands spending £5K per month, there’s a mismatch between their marketing and their actual experience. Similarly, if they claim deep Meta expertise but their case studies are heavily weighted toward Google, dig into why.
Check Third-Party Reviews
Clutch, Google Reviews, and even LinkedIn recommendations can provide unfiltered perspective. Look for reviews that mention specific experiences rather than generic praise. “They helped us increase our MER from 2.8x to 3.6x over six months” is more credible than “great agency, highly recommend.”
What a Genuinely Good Case Study Looks Like
The best case studies from legitimate D2C marketing companies share several traits:
They include both spend and revenue data, not just revenue. They cover a meaningful time period, ideally 6-12 months, not just the best quarter. They acknowledge challenges or setbacks and explain how they were addressed. They use blended metrics rather than platform-only reporting. They name the client or provide enough detail for verification. They explain the strategy behind the results, not just the outcome.
If an agency’s case studies include these elements, you’re probably looking at a team that values transparency over impression management. And that’s the kind of team you actually want handling your ad spend.
The Bottom Line
Case studies should be the starting point of your evaluation, not the deciding factor. Treat them as conversation starters: a reason to dig deeper, ask harder questions, and verify claims through direct contact with real clients. The agencies worth hiring won’t just survive that scrutiny. They’ll welcome it.
