Most "best Flutter agency" lists rank companies on three things: hourly rate, review score and portfolio size. Those are fine filters for a brochure app. For a two-sided marketplace they miss almost everything that makes the project hard: split payments, identity checks, real-time messaging and an architecture that survives growth.

If you're the developer, CTO or technical co-founder asked to vet a Flutter partner, this post gives you a technical interview script instead of a ranking. It's based on the marketplace-specific criteria in Journeyhorizon's guide to choosing a Flutter app development company for marketplaces .

Why Flutter is a reasonable default for marketplaces

Before vetting the partner, sanity-check the stack choice:

One codebase, three targets. iOS, Android and web from a single Dart codebase, with consistent UX for buyers and sellers across devices.

Cost. For many apps, Flutter is roughly 30–40% more cost-efficient than building separate native apps, with comparable performance.…