you cant fix stupid......i would not take a student with only 20 dives ,,,thats just me , as for buying units off e bay i do it all the time no one asked for a card (did it last week ) i have yet to get one that didnt need work , but i KNEW what was wrong..........someone not a tech wont , then they will die ........i try not to be a scubs cop, i try to show in a nice manner the errors of their ways (and usually get them NOT to dive) but as a military buddy says "ya cant fix crazy ,if they really want to die " my 2 cents