Should i be obligated to give him the money back?

About a week ago i sold my b amp to some dude. I thought something was wrong with it prior to the whole transaction so i took it to 3 professionals so they could take a look at it. Daddy's junkie music and my friends guitar teacher both said it was just a loose speaker and wouldn't cost more then $20-30 (for labor) to fix. I took it to a The music workshop in salem and they said they didn't hear anything wrong with it. So, i felt a lot better about selling it to someone... Before the guy took the drive over i told him that i was pretty positive that the speaker was loose and that it was an easy cheap fix... He decided to come anyway. He got here, plugged in and wasplay inn some lines. When theweirdd loose speaker noise came up, i told him that is what was wrong with it and what the professionals had said... He ended up buying it for a good price for what we thought was the condition of the amp... I justreceivedd a call from him saying that he took it to somebody and they said that the speaker was loose, but the speaker was also overheated and would cost $150 to fix.... I honestly had no idea about this and i do feel bad, idon'tt want to rip anybody off... but i no longer have the money he gave me for it and i am in mive (for a teenager) debt... The human side of me wants to help him out but i literally cant.. and the side of me wants to tell him that he agreed to buying it, so he has to deal.... idon'tt want to pay him back obviously... the fact that we agreed to a price and he bought it after i informed him of ALL i know, is that enough to keep this away? Wedidn'tt write up any legal paperwork or anything, all it was was a handshake, thank you, and goodbye... From thevoice maill he left, it sounded like if we cant settle something, he is gonna take legal action... can he even do that? what does he have to go off of?