Start with domain experience, not the length of the client list. Request two or three projects that resemble your domain and your stack, and then ask specifically whether those engineers are still with the .net development company. A solid partner will introduce you to the engineers. Answers that name nobody at this stage generally mean you are talking to a reseller.

The paperwork warrants a slower read than the pitch. Three clauses do most of the work: ownership of the code, the NDA, and termination and handover. All the work product must transfer to you on payment, along with designs, scripts and infrastructure configuration. Watch for any clause that keeps framework code in the vendor's hands, as this is frequently the part you cannot replace later.

Ask where their numbers come from. A serious estimate is accompanied by the assumptions behind it, a breakdown by feature or module and a best case and a worst case. A fixed price is only reasonable when the requirements are stable difference between vue and angular documented; in any other case the vendor prices the risk in and you pay for uncertainty either way. Time and materials moves the risk back to the client, so it requires visible weekly reporting and a spending cap.

The delivery process beats team size. Establish how a new requirement enters the plan, who writes the acceptance criteria and how quality assurance works. A mature team will be able to show you a live build at the end of each sprint. Clear, written acceptance criteria remain the practical protection against the it-was-never-in-scope conversation.

Last, consider the handover at the start rather than at the end. Insist that the repository lives under your account from the first commit, and that documentation is updated as part of the work. A vendor with nothing to hide accepts it without argument; a long negotiation over it reveals quite a lot.