Start with relevant experience, not the number of logos on the website. Request three or four case studies that match your stack, and then ask specifically which engineers actually built it. An honest provider will introduce you to the engineers. Answers that name nobody at this stage almost always mean the demo work came from somewhere else.
The agreement needs more scrutiny than the proposal. Three clauses do most of the work: assignment of intellectual property, non-disclosure, and termination and top angular development company handover. Everything produced has to transfer to you once invoices are settled, including designs, scripts and infrastructure configuration. Look closely at wording that keeps framework code in the vendor's hands, since it is usually the dependency that makes switching painful.
Find out how the estimate was built. An honest estimate arrives with a written set of assumptions, a task-level breakdown and an explicit range. A fixed price only makes sense when the specification is complete; in any other case the supplier adds a risk premium and you pay for uncertainty either way. Time and materials moves the risk back to the client, so it demands visible weekly reporting and a spending cap.
How the work is run matters more than the number of developers. Ask what happens when the scope changes, who signs off on a feature and what the QA setup looks like. A team should be able to walk you through running software development technologies rather than status reports. Acceptance criteria in writing remain the only reliable protection against an argument at delivery time.
Finally, consider the end of the engagement before it becomes urgent. Ask that the code repository sits under your account from the beginning, vue js development services and that a readme and architecture notes are kept current as the code changes. A vendor with nothing to hide will agree quickly; a long negotiation over it tells you quite a lot.