Can a buyer back out with no penalty?

Hi members,

Last week I got an offer for a preamp on Audiogon which I am selling. The buyer offer cash local pickup and he required an audition before taking the preamp. It seems fair to me so I accepted his offer.

Yesterday he came to my house with another guy. They spent almost an hour to play through my system. Then finally they said they don't want to buy it with the reason "I don't like the sound". I tried to explain to him that after the buyers' offer is accepted that is a commitment to buy. Unless the product was not as described in the ads, he has to take it. They just left without saying anything.

My question is: what do we do with that kind of buyer, how to deal with this situation correctly?

Thanks,

Calvin