Start with domain experience, not the size of the portfolio. Ask to see two or hire senior react developers three engagements that resemble your domain and your stack, and then ask which engineers actually built it. A solid partner is happy to connect you with the engineers. Answers that name nobody at this stage usually mean you are talking to a reseller.

The paperwork warrants a slower read than the pitch. Three clauses do most of the work: ownership of the code, non-disclosure, and notice periods and handover. All the work product has to transfer to you as it is paid for, including documentation, react native development agency pipelines and deployment scripts. Watch for wording that keeps so-called reusable libraries in the vendor's hands, as it is usually the part you cannot replace later.

Find out how the estimate was built. An honest estimate arrives with a written set of assumptions, a breakdown by feature or module and a best case and a worst case. A fixed price works only when the scope is genuinely frozen; in any other case the provider pads the number and you pay for it anyway. Hourly billing moves the risk back to the client, so it demands a cap, regular demos and transparent reporting.

Process beats team size. Find out what happens when the scope changes, who writes the acceptance criteria and what the QA setup looks like. A team will be able to walk you through a live build at the end of each sprint. Clear, written acceptance criteria are the practical protection against the it-was-never-in-scope conversation.

Last, think about the day you no longer need this vendor at the start rather than at the end. Require that the source repository sits under your account from day one, and that documentation is updated as part of the work. A vendor with nothing to hide says yes immediately; a long negotiation over it says a great deal.