An estimate that arrives instantly should be treated as a bad sign. Any serious team will come back with questions first: mobile app development services about integrations. A vendor that quotes without asking anything is simply pricing a guess, and the gap resurfaces as a change order — on your budget.
Watch for any distance between the engineers on the sales call and those who eventually appear in the repository. Ask for the names application support and maintenance services CVs of the actual team in the agreement, with a clause about substitutions. A vendor that talks only about abstract roles and refuses to name individuals is preserving its own flexibility at your cost.
Insist on access to the repository from day one. A partner that hands over a build only at the end of each phase is asking you to accept a black box. Visible commits tell you the actual pace far better than any status report. The same holds for the CI pipeline: if it does not exist, promises about quality are nothing more than words.
Ambiguous phrasing around code ownership is not an accident. The contract must state plainly that all deliverables belong to the client on payment. Look too at the jurisdiction and the milestone terms: a large upfront payment with no milestone tied to it removes any leverage you would otherwise keep.
Lastly, pay attention to communication. Confirm how much working-time overlap you will share each day, which person handles your questions and how quickly. Some genuine overlap is usually enough; none at all converts each small question into a day of delay. Unclear written communication in the sales phase does not improve later.