Begin with proven experience, not the size of the portfolio. Request a couple of case studies that match your domain and your stack, and then find out whether those engineers are still with the company. A serious vendor will introduce you to the people who would work on your project. Vague answers at this stage usually mean the demo work came from somewhere else.
The paperwork warrants a slower read than the pitch. Three clauses do most of the work: ownership of the code, non-disclosure, and notice periods and golang web development services handover. Every artifact should transfer to you as it is paid for, together with source code, designs and infrastructure as code. Be careful with any clause that leaves framework code outside the transfer, because that is often the part you cannot replace later.
Ask how they estimate. A serious estimate arrives with the assumptions behind it, a breakdown by feature or module and an explicit range. A fixed-price contract is only reasonable when the requirements are stable and documented; when the scope is still moving the supplier prices the risk in and you pay for it anyway. Time and materials shifts that risk to you, so it requires a cap, regular demos and vue js vs angular transparent reporting.
The delivery process matters more than the number of developers. Establish how change requests are handled, who signs off on a feature and how quality assurance works. A well-run team can demonstrate a working build every one or two weeks. Written acceptance criteria remain the only reliable protection against endless rounds of rework.
Before signing, think about the handover before it becomes urgent. Insist that the source repository stays on infrastructure you own from the beginning, and that a readme and architecture notes are kept current as the code changes. A vendor with nothing to hide says yes immediately; a long negotiation over it says a great deal.
