A quote that comes back within a day is a red flag rather than good service. A competent team responds with questions first: about who owns the data and what happens on failure. A supplier that commits to a figure with no clarification is simply working from a template, and the gap will be corrected later — and you will pay for it.
Look out for a gap between the engineers on the sales call and the developers actually assigned. Request the names and CVs of the actual team in the statement of work, application support services with a clause covering replacement. A provider that talks only about roles and outsource blockchain development refuses to name people is keeping the right to assign anyone it likes.
Ask for access to the repository from day one. A team that hands over nothing between demos is asking you to take delivery on faith. Regular commits and pull requests tell you who is really on the project far better than any status report. The same applies to the automated test suite: if it does not exist, promises about quality are nothing more than words.
Ambiguous contract language around IP is not an accident. The document needs to state in plain terms that all outputs produced under it become the property of the client upon settlement of the relevant invoice. Also check the governing law and how payments are structured: heavy prepayment with no deliverable attached removes the only leverage you have.
Lastly, look at how they communicate. Establish how much working-time overlap you will share with your timezone, who is expected to answer questions and within what time. Some genuine overlap generally works; zero overlap turns every clarification into a lost day. Sloppy written English in the proposal rarely improves under delivery pressure.