Look first at proven experience, not the size of the portfolio. Ask to see two or three case studies that match your stack, and then ask whether those engineers are still with the symfony development company. A serious vendor will put you on a call with the people who would work on your project. Answers that name nobody 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: ownership of the code, confidentiality, laravel livewire vs react and notice periods and handover. Every artifact should transfer to you once invoices are settled, including documentation, pipelines and deployment scripts. Be careful with language that leaves so-called reusable libraries outside the transfer, since it is usually the part you cannot replace later.

Ask how they estimate. An honest estimate is accompanied by a written set of assumptions, a breakdown by feature or module and a best case and a worst case. A fixed-price contract works only when the requirements are stable and documented; when the scope is still moving the provider pads the number and you pay for it anyway. Time and materials puts the risk on your side, so it needs a cap, regular demos and transparent reporting.

Process beats headcount. Ask how change requests are handled, who signs off on a feature and what the QA setup looks like. A well-run team should be able to show you a live build at the end of each sprint. Acceptance criteria in writing stay your only real protection against an argument at delivery time.

Last, think about the end of the engagement at the start rather than at the end. Insist that the repository stays in your organisation from day one, and that a readme and architecture notes are kept current as the code changes. A partner who is comfortable with this will agree quickly; resistance at this point reveals quite a lot.