Can a buyer back out with no penalty?

Breaking contract on a small scale is wrong but not terribly wrong. I believe, negative feedback would violate the principle of adequate reaction in this case.

I've had many very nice knowledgable people visit my home to complete the purchase, listen to the equipment and pay with no problems or worries.

i can understand some people may be nervous having perfect strangers visit tho.

I'm not one of those people. I've been thinking about the previous responses related to a non refundable deposit, and for nervous people that may be a good idea. 

For me, when they accept the offer after we communicate via audiogon, phone or email, I have a pretty good idea about the person I'm dealing with. 

I would thonk honk it very strange that a person would not want me to see or hear the item after accepting my offer for many reasons. 1) it may be a scam. 2) it may not actually work. 3) it may not work or look as advertised and 3) it may be stolen and the seller's home has nothing in it that indicates that the seller knows the first thing about high end audio equipment.

i don't care about the price if it is stolen. I'm walking away. 
Lastly, some equipment is extremely heavy and will cost much to ship. If I'm nearby I would prefer to pick it up myself. 

If if the buyer is nearby, why ship it?  Anyway, just my thoughts. 

Enjoy

Also, I'm fairly confident that I can sell the item in question to someone else. I always price my items to sell so I'm really not worried.  If someone changes their mind after accepting the listed price and then coming by to hear it, so be it. Someone else will buy it. 

Enjoy