Ask who owns the backend, how versions are released, and whether they have shipped store reviews — not only UI mockups.
A business app is clients, APIs, an operator console and a release plan. Vendors who only show screens will discover permissions and payments in week ten. That discovery is not free.
If you also need a heavy back office, you want one delivery group that already designs roles. If you only need a store client on an existing API, ask for that narrower scope. MonkeyTech does both; the estimate should still name which.
A pretty mini program theme does not prove store review skill. If you need both channels, ask how IDs stay shared.
Only if the products truly diverge. Two vendors plus one undocumented API is a common way to buy two sources of truth.
A single freelancer promising a date is a different risk than a team that can test, review and stay for defects. Match the risk to how hard go-live is to undo.
Source, API notes, store accounts ownership, a defect window and what "done" means for each milestone.
Ask a vendor to walk store review and API versioning before you compare day rates. Start that conversation at /en/app/.