Life hack in this area: an account that works from the contractor is physically in the client’s office, goes to sprint planning, grooming, retrospectives, etc. This person understands what the product lives, what kind of culture is, what kind of people work there. Due to such a deep immersion, it is quite easy to select new participants to the team or make replacements - because he understands well what the project needs.
In our practice, there were several cases when we insisted to take a developer, rejected after the interview, for a test period for 1-2 weeks. If he had not passed the trial period, the customer would pay 50% of the cost - we took half of the risks on ourselves. But this has never happened - the developers always justified confidence and remained on the project.
