Begin with domain experience, not the length of the client list. Ask for two or three engagements that resemble your technology stack, and then find out which engineers actually built it. A solid partner is happy to connect you with the tech lead. Vague answers at this stage usually mean the demo work came from somewhere else.

The paperwork warrants more scrutiny than the proposal. A few clauses carry most of the weight: assignment of intellectual property, rust web development confidentiality, and exit terms and handover. Every artifact should transfer to you on payment, including documentation, custom affiliate tracking software pipelines and deployment scripts. Watch for wording that leaves framework code in the vendor's hands, because it is usually the dependency that makes switching painful.

Find out how the estimate was built. A serious estimate is accompanied by the assumptions behind it, a breakdown per feature and a best case and a worst case. A fixed-price contract is only reasonable when the scope is genuinely frozen; in any other case the supplier prices the risk in and you fund the buffer regardless. Time and materials puts the risk on your side, so it requires a cap, regular demos and transparent reporting.

How the work is run matters as much as team size. Find out how a new requirement enters the plan, who writes the acceptance criteria and how testing is organised. A well-run team should be able to demonstrate a working build every one or two weeks. Acceptance criteria in writing are the only reliable protection against the it-was-never-in-scope conversation.

Last, plan for the end of the engagement at the start rather than at the end. Ask that the repository lives in your organisation from the first commit, and that the documentation is refreshed in every sprint. A partner who is comfortable with this says yes immediately; hesitation here says a great deal.