Look first at proven experience, not the number of logos on the website. Ask for a couple of case studies that resemble your domain and your stack, and then ask who actually wrote that code. An honest provider will put you on a call with the tech lead. Answers that name nobody at this stage usually mean you are talking to a reseller.

The paperwork deserves more attention than the sales deck. A few clauses carry most of the weight: ownership of the code, non-disclosure, and termination and handover. Everything produced should transfer to you on payment, along rag system development with langchain source code, designs and infrastructure as code. Be careful with wording that leaves so-called reusable libraries outside the transfer, because it is usually exactly the piece that locks you in.

Ask how they estimate. An honest estimate arrives with the assumptions behind it, a task-level breakdown and a range rather than a single number. A fixed price only makes sense when the scope is genuinely frozen; in any other case the supplier prices the risk in and you pay for it anyway. A time-and-materials model puts the risk on your side, so it requires a sprint cadence, demos and a budget cap.

The delivery process beats the number of hire pytest developers. Ask how a new requirement enters the plan, who signs off on a feature and how quality assurance works. A well-run team will be able to demonstrate running software rather than status reports. Clear, written acceptance criteria are the only reliable protection against the it-was-never-in-scope conversation.

Before signing, think about the end of the engagement before it becomes urgent. Require that the source repository stays in your organisation from the first commit, and that documentation is written as you go rather than left to the end. A vendor with nothing to hide accepts it without argument; a long negotiation over it tells you a great deal.