This is why embedded is better than fully remote teams. Your engineering managers should start building relationships with candidates pre-hire, and then be doing 1:1s post hire. Even with camera off, you'd notice if somebody is not the same person, unless you have too many other responsibilities.
Developers are directly part of the team, reporting to the same engineering manager, rather than being under their own agency manager, pm, etc. You should never be going through an intermediary to work with remote devs that you hire (aside from, perhaps, the handling of payroll & benefits.)
