Look first at relevant experience, not the number of logos on the website. Ask to see two or three projects that sit close to your domain and your stack, and then ask specifically who actually wrote that code. An honest provider will introduce you to the engineers. Evasive answers at this stage usually mean you are talking to a reseller.
The paperwork warrants more scrutiny than the proposal. A few clauses carry most of the weight: ownership of the code, the NDA, and notice periods and swift web framework handover. Every artifact should transfer to you as it is paid for, including source code, designs and infrastructure as code. Look closely at language that keeps reusable components with the vendor, as this is frequently the dependency that makes switching painful.
Ask how they estimate. A credible estimate arrives with a written set of assumptions, a task-level breakdown and a best case and a worst case. A fixed-bid deal works only when the scope is genuinely frozen; otherwise the provider pads the number and you fund the buffer regardless. A time-and-materials model shifts that risk to you, so it requires a cap, regular demos and transparent reporting.
Process matters as much as the number of hire mobile app developers. Ask what happens when the scope changes, who defines done and how quality assurance works. A well-run team should be able to walk you through a working build every one or two weeks. Acceptance criteria in writing remain your only real protection against the it-was-never-in-scope conversation.
Finally, plan for the handover at the start rather than at the end. Require that the code repository lives on infrastructure you own from the beginning, and that the documentation is refreshed in every sprint. A partner who is comfortable with this says yes immediately; hesitation here tells you a great deal.
