Start with proven experience, not the size of the portfolio. Ask to see a couple of engagements that sit close to your stack, and then find out who actually wrote that code. A serious vendor will introduce you to the tech lead. Vague answers at this stage generally mean the delivery team is not the team you were shown.
The agreement warrants a slower read than the pitch. Three sections matter more than the rest: intellectual property assignment, non-disclosure, and notice periods and laravel inertia vs livewire handover. Everything produced must transfer to you once invoices are settled, including documentation, pipelines and deployment scripts. Look closely at any clause that leaves so-called reusable libraries with the vendor, as it is usually the dependency that makes switching painful.
Ask where their numbers come from. A credible estimate comes with a list of assumptions, a breakdown per feature and an explicit range. A fixed-price which contract model for software development works only when the specification is complete; when the scope is still moving the vendor pads the number and you pay for it anyway. Time and materials shifts that risk to you, so it needs visible weekly reporting and a spending cap.
The delivery process matters as much as the number of developers. Find out how change requests are handled, who signs off on a feature and react js development services how quality assurance works. A well-run team should be able to show you running software outsourcing blog rather than status reports. Written acceptance criteria remain the practical protection against the it-was-never-in-scope conversation.
Before signing, plan for the end of the engagement before it becomes urgent. Insist that the code repository lives on infrastructure you own from day one, and that a readme and architecture notes are kept current as the code changes. A provider confident in its own work accepts it without argument; resistance at this point says quite a lot.