An estimate that arrives instantly counts as a warning, not a service level. A competent team will come back with questions first: about who owns the data and what happens on failure. A supplier that prices with no clarification is probably guessing, and a guess will be corrected later — on your budget.
Watch for any distance between the people you meet and those who eventually appear in the repository. Request named engineers in the agreement, offshore development rates with a clause about substitutions. A vendor that talks only about a pool of resources and refuses to name people is reserving the right to assign anyone it likes.
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 take delivery on faith. Visible commits reveal how many people are really working far better than any status report. The same applies to the CI pipeline: if it does not exist, quality claims remain nothing more than words.
Vague phrasing around IP is rarely an oversight. The contract should state in plain terms that all deliverables belong to your business upon settlement of the relevant invoice. Look too at the jurisdiction and the milestone terms: a large upfront payment with nothing due in return for weeks removes any leverage you would otherwise keep.
Last, hire offshore flutter developers pay attention to how they communicate. Confirm what overlap you will share with your timezone, who is expected to answer day-to-day questions and on what response times. Four hours of overlap generally works; zero overlap stretches every clarification into a twenty-four hour round trip. Sloppy written English in the early emails rarely improves later.