I agree, I am not trying to be argumentative, but I am sorry, you can not tell if a guitar is going to lose it's tune in 15 - 20 minutes of playing. Some may be fine for an hour, then next time you pick it up it has faulted, I am not on the side of buyer or seller, just think it could be a problem the seller was NOT aware of as they admitted to not playing it themselves for longer than 5 minutes at a time. Face it, who knows? who thinks? it is the OP's call, I was just saying for the sake of saving themselves a neg - I (personally) would refund - less said charges etc.