An estimate that arrives instantly is a red flag rather than good service. An experienced provider responds with clarifying questions before any number: about users and volumes. A vendor that prices without asking anything is simply working from a template, and a guess resurfaces as a change order — at your expense.
Look out for any distance between the people you meet and those who eventually appear in the repository. Request the names and CVs of the actual team in the contract, with a provision covering replacement. A team that will only describe a pool of resources and never names specific engineers is reserving the right to assign anyone it likes.
Require commit-level visibility from the start. A provider that shows nothing between demos is inviting you to take delivery on faith. Daily commits show you the actual pace far better than a slide deck. The same applies to the CI pipeline: if nothing runs automatically, assurances about quality remain just talk.
Vague phrasing around code ownership is not an oversight. The document should state plainly that the code, blockchain development agency designs and documentation belong to your company on payment. Look too at which country's law applies and turnkey software development services how payments are structured: heavy prepayment with no milestone tied to it takes away any leverage you would otherwise keep.
Lastly, examine how they communicate. Confirm what overlap the teams will share with your timezone, which person answers your questions and on what response times. Some genuine overlap is normally sufficient; none at all stretches every clarification into a lost day. Unclear written communication in the early emails will not improve later.