Start with relevant experience, not the number of logos on the website. Ask for two or three case studies that match your stack, extranet development qatar and then ask specifically who actually wrote that code. A serious vendor will put you on a call with the people who would work on your project. Vague answers at this stage almost always mean the delivery team is not the team you were shown.
The contract needs more scrutiny than the proposal. Three sections matter more than the rest: intellectual property assignment, non-disclosure, and notice periods and handover. Everything produced should transfer to you as it is paid for, together with designs, scripts and infrastructure configuration. Be careful with language that keeps so-called reusable libraries outside the transfer, as it is usually the dependency that makes switching painful.
Ask where their numbers come from. An honest estimate is accompanied by the assumptions behind it, a task-level breakdown and a best case and a worst case. A fixed-bid deal works only when the requirements are stable and documented; in any other case the provider pads the number and you fund the buffer regardless. Hourly billing moves the risk back to the client, so it needs a cap, regular demos and transparent reporting.
How the work is run beats team size. Find out how change requests are handled, who signs off on a feature and how testing is organised. A team will be able to walk you through a working build every one or custom llm development two weeks. Clear, written acceptance criteria stay your only real protection against an argument at delivery time.
Last, plan for the handover while the relationship is still good. Ask that the code repository sits in your organisation from day one, outsource mobile app development and that the documentation is refreshed in every sprint. A provider confident in its own work says yes immediately; resistance at this point tells you quite a lot.