I'm still mystified...

No that’s not what they are doing. The people upset with sellers who add Paypal fees in their Audiogon ads but do not apply this reasoning to other products and services they purchase are using poor judgement about what is important and what is not and are unlikely to confront business owners or utilities or government agencies about excessive or undisclosed charges, IMHO. That is their right, but they may miss out on some really good audio deals over nothing, IMHO.

It works both ways. If somebody wants to come by and pay cash, should they have to pay the full price with PayPal fees included in the price? If somebody sees a paypal surcharge, then pay by check and don’t pay the fee. It’s the buyers choice.
Also, when you go buy a car, you don’t know what the out the door price is until you know what taxes you will be paying, registration fees, etc.. all you know is the cost before all the fees/taxes attached.
Have you ever tried to buy an expensive item with a credit card? Some dealers will want to try and charge you for the credit card cost. It all depends on the markup and what they make on the transaction if they can pay the fee or not.

It’s all negotiable and all that matters is the out the door price. 

OK.  Don't buy.  Sounds like a good solution.

What's the difficulty here guys?  Just add the 3% to your asking price and offer a 3% discount for cash.  Simple stuff seeing as both PayPal and Visa/MC don't allow merchants to upcharge for using their services.  I'm surprised Audiogon hasn't stopped the ridiculous 3% upcharge crap considering the potential problems.