Look first at domain experience, not the size of the portfolio. Request a couple of case studies that sit close to your domain and your stack, and then ask specifically whether those engineers are still with the company. A solid partner will put you on a call with the people who would work on your project. Answers that name nobody at this stage usually mean the demo work came from somewhere else.

The agreement needs more scrutiny than the proposal. Three sections matter more than the rest: intellectual property assignment, the NDA, and termination and handover. All the work product has to transfer to you on payment, together with designs, hire dedicated php developers scripts and infrastructure configuration. Be careful with language that leaves so-called reusable libraries in the vendor's hands, because that is often exactly the piece that locks you in.

Find out how the estimate was built. A serious estimate comes with the assumptions behind it, a task-level breakdown and a best case and a worst case. A fixed price only makes sense when the scope is genuinely frozen; in any other case 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.

The delivery process matters more than headcount. Establish how a new requirement enters the plan, who defines done and how testing is organised. A mature team will be able to walk you through a live build at the end of each sprint. Acceptance criteria in writing are the only reliable protection against endless rounds of rework.

Last, consider the end of the engagement at the start rather than at the end. Ask that the repository lives on infrastructure you own from day one, rust development services and that documentation is written as you go rather than left to the end. A vendor with nothing to hide accepts it without argument; hesitation here reveals a great deal.