Start with domain experience, not the size advantages of laravel vs wordpress the portfolio. Request three or four projects that match your stack, and outsource real estate development then ask which engineers actually built it. A serious vendor will introduce you to the tech lead. Vague answers at this stage almost always mean the delivery team is not the team you were shown.
The contract warrants a slower read than the pitch. Three clauses do most of the work: intellectual property assignment, non-disclosure, and notice periods and handover. Every artifact should transfer to you as it is paid flutter developer for hire, together with documentation, pipelines and deployment scripts. Be careful with any clause that keeps framework code with the vendor, since it is usually the dependency that makes switching painful.
Find out how the estimate was built. A serious estimate comes with the assumptions behind it, a task-level breakdown and top react native development companies a range rather than a single number. A fixed price works only when the scope is genuinely frozen; in any other case the provider adds a risk premium and you pay for uncertainty either way. A time-and-materials model puts the risk on your side, so it needs visible weekly reporting and a spending cap.
How the work is run matters more than headcount. Establish how change requests are handled, who signs off on a feature and how quality assurance works. A mature team will be able to show you a working build every one or two weeks. Written acceptance criteria stay the only reliable protection against an argument at delivery time.
Last, think about the day you no longer need this vendor while the relationship is still good. Insist that the code repository sits under your account from the first commit, and that the documentation is refreshed in every sprint. A vendor with nothing to hide says yes immediately; a long negotiation over it tells you most of what you need to know.