Start with relevant experience, not the length of the client list. Ask for laravel vs next js two or three engagements that match your domain and your stack, and then ask specifically who actually wrote that code. A solid partner will put you on a call with the people who would work on your project. Evasive answers at this stage usually mean the demo work came from somewhere else.
The contract needs more scrutiny than the proposal. Three clauses do most of the work: assignment of intellectual property, confidentiality, and termination and handover. Everything produced must transfer to you on payment, including source code, sla based software support designs and infrastructure as code. Be careful with language that leaves so-called reusable libraries in the vendor’s hands, since this is frequently the dependency that makes switching painful.
Ask where their numbers come from. A serious estimate comes with a list of assumptions, a breakdown per feature and a best case and a worst case. A fixed-bid deal only makes sense when the requirements are stable and documented; when the scope is still moving the supplier adds a risk premium and you pay for it anyway. Hourly billing shifts that risk to you, so it needs a sprint cadence, demos and lms development company a budget cap.
Process matters more than headcount. Find out what happens when the scope changes, who writes the acceptance criteria and how quality assurance works. A mature hire dedicated development team can show you running software rather than status reports. Clear, written acceptance criteria stay your only real protection against endless rounds of rework.
Finally, consider the end of the engagement while the relationship is still good. Require that the code repository stays in your organisation from the beginning, and that documentation is written as you go rather than left to the end. A vendor with nothing to hide accepts it without argument; resistance at this point reveals most of what you need to know.