Begin with relevant experience, affiliate software development company not the length of the client list. Ask for two or three engagements that resemble your domain and your stack, and then ask specifically which engineers actually built it. An honest provider will put you on a call with the tech lead. Answers that name nobody at this stage usually mean the delivery team is not the team you were shown.
The agreement deserves more attention than the sales deck. A few clauses carry most of the weight: intellectual property assignment, non-disclosure, and termination and handover. Every artifact has to transfer to you once invoices are settled, including documentation, pipelines and deployment scripts. Look closely at wording that keeps so-called reusable libraries with the vendor, since this is frequently the part you cannot replace later.
Ask how they estimate. An honest estimate is accompanied by the assumptions behind it, a breakdown per feature and a best case and a worst case. A fixed-price contract works only when the specification is complete; in any other case the provider adds a risk premium and you pay for uncertainty either way. A time-and-materials model puts the risk on your side, so it demands a cap, offshore development rates regular demos langchain and rag difference transparent reporting.
How the work is run matters more than headcount. Establish what happens when the scope changes, who signs off on a feature and how quality assurance works. A team will be able to demonstrate a live build at the end of each sprint. Clear, written acceptance criteria stay the practical protection against endless rounds of rework.
Finally, plan for the handover before it becomes urgent. Insist that the code repository lives on infrastructure you own from day one, and that a readme and architecture notes are kept current as the code changes. A vendor with nothing to hide will agree quickly; resistance at this point reveals a great deal.