Its really just academic unless there is an accident and the 'checker' who the 'checkee' thought was in command changes his mind and the 'checkee' finds himself as P1. There is an incentive for this kind of thing: most insurers wont cover anyone whose had an accident in the last 5 years.
Clubs and Groups that operate as Ltd companies offer much more protection when things go bad but co-owning groups operating on the 'cheap' co-opting other co-owners to do check rides are open to all manner of abuse and normally this will only surface after an 'event'