An estimate that arrives instantly should be treated as a red flag rather than good service. An experienced provider responds with a list of questions: about integrations. A provider that quotes without asking anything is simply working from a template, kotlin web development company and that guess will be corrected later — and you will pay software development for fintech it.
Be wary of any distance between the engineers on the sales call and those who eventually appear in the repository. Insist on specific people rather than roles in the statement of work, with a clause covering replacement. A team that talks only about a pool of resources and refuses to name people is reserving the option to staff you with whoever is free.
Insist on commit-level visibility from the first week. A provider that hands over a build only at the end of each phase is inviting you to take delivery on faith. Daily commits tell you how many people are really working far better than any status report. The same applies to the automated test suite: if nothing runs automatically, quality claims are just talk.
Loose wording in the contract around code ownership is never an oversight. The contract should state explicitly that all deliverables transfer to your business on payment. Check also the jurisdiction and monolith or microservices the milestone terms: heavy prepayment with no deliverable attached takes away the only leverage you have.
Last, examine communication. Ask how much working-time overlap the teams will share each day, who handles your questions and on what response times. A few hours of overlap is normally sufficient; zero overlap converts every clarification into a day of delay. Sloppy written English in the proposal will not improve once the work starts.