What sort of trouble could one get into selling shared details? Would one possibly be sued by Netflix or even if the accounts are hacked, could one be charged with selling stolen goods? And if so whom by? The police?
It wouldn't be legal to sell a shared account if a shared account was actually legal in the first place. The contract is between Netflix and the account holder, so if the account holder provided the details to others they would be voiding their contract and if their details were obtained without their consent then that would be unlawful.