A number produced without questions should be treated as a warning, not a service level. An experienced provider will come back with a list of questions: about who owns the data and what happens on failure. A vendor that commits to a figure before understanding the scope is guessing, and that guess resurfaces as a change order — at your expense.
Watch for any distance between the people you meet and the people who will code. Ask for named engineers in the statement of work, with wording about substitutions. A team that will only describe a pool of resources and which is better livewire or react refuses to name individuals is keeping its own flexibility at your cost comparison nearshore vs offshore development.
Ask for commit-level visibility from the first week. A partner that shows code only at milestones is asking you to take delivery on faith. Visible commits reveal who is really on the project far better than a slide deck. The same applies to the CI pipeline: if there is no pipeline, quality claims are nothing more than words.
Ambiguous contract language around intellectual property is never an accident. The agreement must state explicitly that all outputs produced under it belong to the client on payment. Check also the jurisdiction and the milestone terms: heavy prepayment with no deliverable attached removes the only leverage you have.
Lastly, examine the working rhythm. Establish how much working-time overlap the teams will share with your timezone, who handles questions and how quickly. Some genuine overlap is usually enough; none at all converts a five-minute question into a day of delay. Sloppy written English in the sales phase will not improve under delivery pressure.