I admittedly have never bought used audio equipment from a private seller, but I have bought and sold used cars privately a few times. My take on this is that once a price is agreed upon as well as a date and time to consummate the sale, the seller should make it clear whether he wants either full or partial payment in advance to guarantee the transaction. It’s not up to the buyer to make an offer to do so since the seller controls the terms of sale. A potential buyer can only meet the seller’s requirements if he knows what they are. I understand that in this case the seller apparently tried to let the buyer know that he had another offer, but under the circumstances of the prior agreement I think he should have given the original buyer more time to respond.
As far as there being "no honor in capitalism", that's a pretty jaded view. And if it's true, then why is a company's good will worth something when it's sold? A business that mistreats its customers will usually not be in business for long.

