The contract deserves a slower read than the pitch. A few clauses carry most of the weight: ownership of the code, non-disclosure, and exit terms and handover.
Last, look at communication. Confirm how many hours the teams will share with your working day, who is expected to answer your questions and how quickly. Four hours of overlap is usually enough; zero overlap turns every clarification into a lost day.
The delivery process beats team size. Ask how a new requirement enters the plan, who signs off on a feature and how quality assurance works. A team can demonstrate a live build at the end of each sprint.