A number produced without questions counts as a warning, not a service level. Any serious team responds with questions first: about users and custom software development price volumes. A vendor that commits to a figure with no clarification is probably pricing a guess, and the gap will be corrected later — and you will pay for it.
Watch for a gap between the people you meet and those who eventually appear in the repository. Ask for specific people rather than roles in the agreement, with a clause covering replacement. A vendor that will only describe roles and will not commit to specific engineers is preserving the right to assign anyone it likes.
Insist on commit-level visibility from the first week. A partner that hands over code only at milestones is inviting you to accept a black box. Visible commits show you the actual pace far better than any status report. The same holds for the automated test suite: if there is no pipeline, promises about quality are nothing more than words.
Loose wording in the contract around intellectual property is never an oversight. The contract should state explicitly that all outputs produced under it transfer to the client on payment. Check also the jurisdiction and how much does it cost to build an app payments are structured: a large upfront payment with no milestone tied to it eliminates any leverage you would otherwise keep.
Finally, examine the working rhythm. Ask what overlap the teams will share each day, which person handles day-to-day questions and how quickly. A few hours of overlap is usually enough; zero overlap converts a five-minute question into a twenty-four hour round trip. Unclear written communication in the proposal does not improve once the work starts.