An estimate that arrives instantly should be treated as a red flag rather than good service. Any serious team responds with a list of questions: about integrations. A vendor that quotes with no clarification is simply guessing, and that guess becomes a change request later — at your expense.
Look out for a gap between the engineers on the sales call and the developers actually assigned. Ask for specific people rather than roles in the statement of work, with a provision that requires notice before anyone is swapped. A team that talks only about roles and refuses to name specific engineers is reserving the option to staff you with whoever is free.
Insist on commit-level visibility from the start. A team that delivers a build only at the end of each phase is inviting you to accept a black box. Regular commits and pull requests show you the actual pace far better than any status report. The same applies to the build and deployment setup: typescript frameworks if there is no pipeline, promises about quality are just talk.
Loose phrasing around code ownership is not an oversight. The contract should state plainly that all deliverables become the property of your company on payment. Check also the jurisdiction and hire ai developers the milestone terms: a large upfront payment with no milestone tied to it takes away your only leverage.
Finally, examine the working rhythm. Ask how much working-time overlap the teams will share with your working day, who is expected to answer day-to-day questions software maintenance and support services within what time. Four hours of overlap is usually enough; no overlap converts every clarification into a lost day. Sloppy written English in the early emails will not improve later.