Start with relevant experience, not the size of the portfolio. Request two or three case studies that sit close to your stack, and then ask who actually wrote that code. A solid partner is happy to connect you with the tech lead. Answers that name nobody at this stage usually mean the demo work came from somewhere else.
The agreement warrants more scrutiny than the proposal. A few clauses carry most of the weight: assignment of intellectual property, non-disclosure, and termination and handover. Everything produced must transfer to you as it is paid for, including documentation, pipelines and deployment scripts. Look closely at wording that leaves reusable components with the vendor, because this is frequently the part you cannot replace later.
Ask where their numbers come from. A credible estimate is accompanied by a list of assumptions, a breakdown by feature or module and a best flutter development company case and a worst case. A fixed-price contract works only when the requirements are stable langchain and rag difference documented; when the scope is still moving the vendor adds a risk premium and you pay for uncertainty either way. Time and materials moves the risk back to the client, so it needs a sprint cadence, demos and a budget cap.
The delivery process matters more than the number of hire flutter developers. Find out how change requests are handled, who defines done and how testing is organised. A well-run team will be able to walk you through a working build every one or two weeks. Acceptance criteria in writing remain the practical protection against endless rounds of rework.
Last, plan for the day you no longer need this vendor before it becomes urgent. Insist that the source repository sits on infrastructure you own from the beginning, and that documentation is written as you go rather than left to the end. A provider confident in its own work accepts it without argument; a long negotiation over it reveals a great deal.
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