A quote that comes back within a day counts as a bad sign. A competent team will come back with questions first: about users and volumes. A supplier that prices before understanding the scope is simply working from a template, and a guess will be corrected later — on your budget.
Look out for a gap between the engineers on the sales call and devops services company the people who will code. Ask for the names and CVs of the actual team in the contract, with a clause about substitutions. A provider that only offers roles and never names individuals is reserving the option to staff you with whoever is free.
Require the source repository from day one. A partner that delivers a build only at the end of each phase is asking you to take delivery on faith. Daily commits show you how many people are really working far better than a slide deck. The same holds for the build and deployment setup: if nothing runs automatically, promises about quality are nothing more than words.
Ambiguous wording in the contract around IP is never an accident. The agreement must state plainly that the code, designs and documentation belong to your business as they are paid for. Look too at the governing law and how much does custom software development cost payments are structured: a request for most of the money up front with no deliverable attached eliminates the only leverage you have.
Finally, look at how they communicate. Confirm what overlap the teams will share with your timezone, which person answers your questions and on what response times. Four hours of overlap is normally sufficient; zero overlap stretches each small question into a lost day. Careless writing in the proposal does not improve under delivery pressure.