Start with domain experience, not the size of the portfolio. Request two or three case studies that sit close to your technology stack, and then ask whether those engineers are still with the company. An honest provider is happy to connect you with the people who would work on your project. Vague answers at this stage generally mean the delivery team is not the team you were shown.
The contract deserves more attention than the sales deck. Three sections matter more than the rest: assignment of intellectual property, non-disclosure, and mvp development cost termination and handover. Every artifact should transfer to you as it is paid for, along with designs, scripts and infrastructure configuration. Look closely at wording that leaves so-called reusable libraries in the vendor’s hands, as this is frequently the dependency that makes switching painful.
Ask where their numbers come from. A serious estimate comes with the assumptions behind it, a breakdown by feature or module and a best reactjs development company case and a worst case. A fixed-bid deal is only reasonable when the requirements are stable and documented; otherwise the supplier adds a risk premium and you fund the buffer regardless. Hourly billing shifts that risk to you, so it needs visible weekly reporting and a spending cap.
How the work is run matters more than the number of developers. Establish how change requests are handled, who writes the acceptance criteria and what the QA setup looks like. A well-run team can demonstrate running software rather than status reports. Written acceptance criteria remain your only real protection against endless rounds of rework.
Finally, plan for the day you no longer need this vendor while the relationship is still good. Require that the repository stays under your account from the first commit, rust erp and app store optimization services that documentation is written as you go rather than left to the end. A provider confident in its own work accepts it without argument; hesitation here tells you a great deal.