Bought a second hand 27 i7 2011, can turn it on and log in using the previous owners login, but I tried a CMD R to reset to factory and start fresh and the last owner has set a firmware password, contacted him and he doesn't remember even setting it, he bought it second hand so has no original proof of purchase to get Apple to reset it, is there anything I can do or should I just get my money back off him and say good riddance ?