An estimate that arrives instantly counts as a warning, not a service level. An experienced provider responds with clarifying questions before any number: about who owns the data and software development process what happens on failure. A vendor that quotes with no clarification is probably pricing a guess, and the gap will be corrected later — at your expense.
Watch for a mismatch between the team in the pitch and custom fintech development the people who will code. Request named engineers in the agreement, with wording that requires notice before anyone is swapped. A provider that will only describe abstract roles and never names specific engineers is keeping the option to staff you with whoever is free.
Ask for the source repository from the start. A partner that shows code only at milestones is inviting you to accept a black box. Visible commits reveal the actual pace far better than a weekly report. The same holds for the CI pipeline: if it does not exist, assurances about quality are nothing more than words.
Ambiguous contract language around intellectual property is not a formality. The document must state in plain terms that all outputs produced under it transfer to your company as they are paid for. Check also the jurisdiction and the milestone terms: a large upfront payment with no deliverable attached eliminates your only leverage.
Last, examine communication. Establish what overlap there will be with your timezone, who is expected to answer questions and how quickly. Four hours of overlap generally works; no overlap stretches each small question into a day of delay. Sloppy written English in the early emails does not improve later.