Look first at proven experience, not the number of logos on the website. Request three or four case studies that match your domain and your stack, and then ask specifically whether those engineers are still with the aws web development company. A solid partner will introduce you to the engineers. Vague answers at this stage almost always mean the delivery team is not the team you were shown.
The contract warrants more scrutiny than the proposal. A few clauses carry most of the weight: intellectual property assignment, non-disclosure, and termination and handover. Everything produced must transfer to you once invoices are settled, together with designs, scripts and top flutter development companies infrastructure configuration. Watch for language that leaves framework code outside the transfer, since it is usually the dependency that makes switching painful.
Find out how the estimate was built. A serious estimate is accompanied by a written set of assumptions, a breakdown per feature and a best case and a worst case. A fixed price only makes sense when the scope is genuinely frozen; when the scope is still moving the provider adds a risk premium and you fund the buffer regardless. Hourly billing puts the risk on your side, so it demands a sprint cadence, demos and a budget cap.
Process matters as much as team size. Establish what happens when the scope changes, who defines done and how quality assurance works. A mature team can walk you through a live build at the end of each sprint. Clear, written acceptance criteria remain the practical protection against the it-was-never-outsourcing versus in house software development-scope conversation.
Finally, think about the day you no longer need this vendor hire angular audit experts before it becomes urgent. Require that the code repository lives on infrastructure you own from day one, and that documentation is updated as part of the work. A vendor with nothing to hide accepts it without argument; a long negotiation over it says most of what you need to know.