hmmmmm, fried tuner?

ok i have this lanzar indash screen right? so it has the screen, a seperate tuner/reciever and a seperate dvd player... so it was installed in somebody esles car and worked, so then i sold it to some other kidd , and he siad when the guy was uptting it in the tuner started to smoke and stuff so now he wants his money back.. and i DON'T wanna give him his money, is there anyway that could be a bad reciever or just a bad job on putting it in (he had it "professionally" done i think).