Highlight the required time and try to study all the documents that the developer must present to you. Pay special attention to the form of the contract. The safest agreement is considered to be the safest. In any case, it is worth studying the contract. It will be best to attract a professional lawyer. If the developer refuses to give you any documents, or does not want to give an agreement for study outside the office, it is worth thinking ten times, if not about conscientiousness, then about the reliability of such a developer.