An estimate that arrives instantly counts as a red flag rather than good service. An experienced provider responds with a list of questions: about users and volumes. A provider that commits to a figure before understanding the scope is probably guessing, and that guess becomes a change request later — on your budget.
Watch for a gap between the engineers on the sales call and those who eventually appear in the repository. Request named engineers in the contract, software maintenance and support services with a provision that requires notice before anyone is swapped. A team that will only describe abstract roles and never names individuals is reserving its own flexibility at your cost.
Insist on commit-level visibility from the start. A team that hands over a build only at the end of each phase expects you to accept a black box. Visible commits show you how many people are really working far better than a weekly report. This extends to the automated test suite: hire a software developer if it does not exist, assurances about quality are just talk.
Loose contract language around intellectual property is never an oversight. The agreement needs to state plainly that all outputs produced under it transfer to the client on payment. Also check which country's law applies and the milestone terms: a request for most of the money up front with no milestone tied to it takes away your only leverage.
Lastly, pay attention to communication. Confirm how many hours there will be with your working day, which named person is expected to answer your questions and how quickly. A few hours of overlap generally works; zero overlap converts every clarification into a day of delay. Careless writing in house vs outsourcing software development the early emails will not improve under delivery pressure.