Begin with relevant experience, not the number of logos on the website. Request three or four case studies that match your domain and your stack, and then ask specifically whether those engineers are still with the company. An honest provider will introduce you to the tech lead. Evasive answers at this stage almost always mean the demo work came from somewhere else.

The paperwork warrants more attention than the sales deck. Three sections matter more than the graphql vs rest: software development outsourcing trends ownership of the code, the NDA, and notice periods and handover. All the work product must transfer to you on payment, together with designs, swift development agency scripts and infrastructure configuration. Look closely at any clause that leaves reusable components outside the transfer, as it is usually the part you cannot replace later.

Ask how they estimate. An honest estimate comes with a written set of assumptions, a breakdown per feature and a range rather than a single number. A fixed price is only reasonable when the requirements are stable and documented; otherwise the provider adds a risk premium and you fund the buffer regardless. Time and materials puts the risk on your side, so it demands visible weekly reporting and a spending cap.

The delivery process beats headcount. Ask how a new requirement enters the plan, who defines done and what the QA setup looks like. A team can show you a working build every one or two weeks. Acceptance criteria in writing remain the only reliable protection against an argument at delivery time.

Last, plan for the end of the engagement at the start rather than at the end. Ask that the source repository sits on infrastructure you own from day one, and that the documentation is refreshed in every sprint. A partner who is comfortable with this will agree quickly; a long negotiation over it reveals quite a lot.