Begin with domain experience, not the size of the portfolio. Ask for three or four engagements that match your stack, and then ask specifically who actually wrote that code. A solid partner will introduce you to the engineers. Evasive answers at this stage usually mean you are talking to a reseller.
The paperwork needs a slower read than the pitch. Three clauses do most of the work: intellectual property assignment, non-disclosure, and termination and vue js software handover. Every artifact must transfer to you once invoices are settled, along with documentation, pipelines and deployment scripts. Watch for language that keeps framework code outside the transfer, since this is frequently the dependency that makes switching painful.
Ask how they free development estimate. A credible estimate arrives with the assumptions behind it, a breakdown per feature and a range rather than a single number. A fixed price works only when the requirements are stable and documented; when the scope is still moving the provider prices the risk software development company in qatar and you pay for it anyway. A time-and-materials model moves the risk back to the client, so it requires visible weekly reporting and a spending cap.
Process matters more than headcount. Establish how a new requirement enters the plan, who signs off on a feature and how testing is organised. A mature dedicated team outsourcing should be able to show you a working build every one or two weeks. Written acceptance criteria stay your only real protection against endless rounds of rework.
Finally, think about the end of the engagement before it becomes urgent. Require that the source repository stays on infrastructure you own from the beginning, and that documentation is written as you go rather than left to the end. A partner who is comfortable with this says yes immediately; resistance at this point reveals most of what you need to know.