A quote that comes back within a day is a red flag rather than good service. Any serious team returns a list of questions: about who owns the data and software livewire what happens on failure. A vendor that commits to a figure without asking anything is probably working from a template, and that guess becomes a change request later — and you will pay for it.
Watch for any distance between the team in the pitch and those who eventually appear in the repository. Request the names and CVs of the actual team in the agreement, with a clause that requires notice before anyone is swapped. A provider that will only describe a pool of resources and never names people is keeping its own flexibility at your cost.
Ask for access to the repository from day one. A team that shows code only at milestones is inviting you to take delivery on faith. Regular commits and pull requests tell you who is really on the project far better than a weekly report. The same applies to the build and deployment setup: if it does not exist, promises about quality are unverifiable.
Vague phrasing around intellectual property is rarely an accident. The contract must state explicitly that all outputs produced under it become the property of the client upon settlement of the relevant invoice. Check also the jurisdiction and the payment schedule: a request for most of the money up front with no deliverable attached eliminates your only leverage.
Last, pay attention to how they communicate. Establish how many hours there will be with your working day, which named person is expected to answer your questions and global software development company within what time. Four hours of overlap is usually enough; none at all stretches each small question into a twenty-four hour round trip. Sloppy written English in the proposal will not improve once the work starts.