Shopify's app store and partner directory list thousands of agencies willing to take your money. Most of them have built a nice-looking store on standard Shopify. A meaningfully smaller number have actually shipped a Shopify Plus project: Functions, native B2B, a real migration off Magento with tens of thousands of orders in the history, a headless storefront that didn't fall over on launch day. Telling those two groups apart before you sign a contract is the entire job of this guide.
The Tell That Separates Them
Ask any Shopify agency to show you a live store they built that's still running on Plus, and watch how quickly a real answer comes back. Agencies with genuine Plus experience will hand you URLs without hesitation, because they're proud of the work and it's easy to verify. Agencies stretching a standard-Shopify portfolio to sound like Plus experience tend to get vaguer here, talking about "enterprise clients" without naming them, or pointing to a case study that turns out to be a theme install with a logo swap.
It's not a perfect test. Some agencies have legitimate NDAs. But paired with a second question, ask them to describe a specific Shopify Functions or checkout customisation they've built, and the gap between real and rehearsed becomes obvious fast. Functions and Scripts are Plus-specific capabilities; an agency that's actually used them has a real story with real constraints they had to work around. An agency that hasn't will talk in generalities.
The Three Ways This Goes Wrong
The theme shop mistake. You hire a team that's excellent at customising Dawn or a premium theme, and genuinely, for a lot of standard Shopify stores, that's all you need. But if your requirements involve B2B wholesale, complex checkout logic, or an ERP integration, a theme customisation team without Plus-specific experience will hit a wall they didn't know was there, usually a few weeks into the build, and either build a fragile workaround or come back asking for more budget.
The lock-in mistake. Some agencies structure the relationship so the store is difficult to leave: code held in their own accounts rather than yours, custom apps with no documentation, a "we'll always maintain it" pitch that quietly becomes the only viable maintenance option. Ask directly, before signing, who owns the theme code and where it lives. A good agency answers this without hesitation, because the honest answer is "you do, and here's the repository."
The headless-by-default mistake. Headless and Hydrogen get pitched aggressively because they're a bigger, more impressive-sounding project. For most stores, a well-built standard Liquid theme is faster to ship, cheaper to run, and entirely capable of hitting strong Core Web Vitals. Headless earns its cost when there's a specific reason for it, an omnichannel requirement, a shared design system, sub-100ms performance targets a theme genuinely can't reach. An agency recommending headless before understanding your actual requirements is optimising for their project size, not your outcome.
What a Real Scoping Conversation Sounds Like
It starts with questions about your business, not your wireframes. What's your current GMV and order volume. Are you running B2B alongside D2C, or planning to. What's actually broken about your current setup, slow pages, a platform you've outgrown, a migration you're dreading. A team that jumps straight to "here's our process" without asking any of this is selling a template, however polished the deck looks.
It also includes an honest conversation about what you don't need. We've talked clients out of headless builds, out of unnecessary app subscriptions, out of full replatforms when a targeted rebuild would solve the actual problem for a third of the cost. If every conversation with an agency ends in "yes, and here's the bigger package," that's worth noticing.
A quick gut check before any contract: if you removed the agency's logo from their proposal, would it still sound specific to your business, or could you swap in any other merchant's name without changing a sentence? Generic proposals produce generic builds.
What It Should Cost
A full custom Shopify Plus build typically starts around $40,000. That covers discovery, a custom theme, and a handful of core integrations. Theme customisation on an existing store, rather than a ground-up rebuild, can come in lower, from roughly $15,000 to $25,000. Headless Hydrogen work, because it involves building and maintaining a genuinely separate frontend application, generally starts around $80,000. Ongoing retainer support for post-launch development typically runs from $8,000 to $10,000 a month.
Quotes well under these ranges for work described as fully custom are worth a second look, not because cheap is automatically bad, but because the gap is usually explained by a template with surface customisation rather than a build engineered around your specific catalogue and workflows.
Before You Sign Anything
Get the migration and SEO plan in writing if you're moving off another platform, not a verbal assurance that "we handle redirects." Get a straight answer on code ownership. Ask what happens if the relationship ends after launch, whether the store keeps functioning cleanly with a different team, or whether critical pieces only that agency understands. None of this is adversarial to ask. A team confident in their own work answers all of it without flinching.
If you're still weighing whether Shopify Plus is even the right tier, our Hydrogen vs standard Shopify breakdown and Shopify B2B guide are worth reading before the agency conversation starts, so you're evaluating proposals against your own understanding, not just theirs.
FAQ
What's the difference between a Shopify agency and a Shopify Plus agency?
A Shopify agency typically works on standard Shopify: theme installs, app configuration, small customisations. A Shopify Plus agency works with the enterprise tier's specific capabilities, Shopify Functions, Scripts, native B2B, multi-store expansion, checkout customisation, and the migration and integration complexity that comes with $1M+ GMV merchants. The skill sets overlap but aren't the same, and a lot of agencies market themselves as the second while only really having done the first.
How do I know if an agency has actually built on Shopify Plus before?
Ask for stores they've built that are still live and still on Shopify Plus, not screenshots from a portfolio, actual URLs you can visit. Ask what GMV range their typical client is in. Ask them to describe a specific Shopify Functions or Scripts use case they've shipped. Vague answers to any of these usually mean standard-Shopify experience being marketed as Plus experience.
What's a realistic budget for a Shopify Plus build?
A full custom Shopify Plus storefront typically starts around $40,000. Theme customisation on an existing store, rather than a full rebuild, can start lower, around $15,000 to $25,000. Headless Hydrogen builds, which add a separate frontend layer, generally start around $80,000. Quotes meaningfully below these ranges for genuinely custom work usually mean a template with light customisation, not a bespoke build.
Should I worry about being locked into an agency after launch?
You should ask about it directly before signing anything. Confirm you own the theme code outright, that it's handed over in a clean repository, not held hostage in the agency's private account, and that documentation exists for any custom apps or Functions they build. An agency that's cagey about code ownership is telling you something about the relationship they intend to have with you after launch.