Personally, I don’t see the difference. If the costs for shipping and paypal fees are listed clearly in the BST thread, are we asking all that much for the buyer to simply add?
However you want to discount it, isn’t it up to the buyer and the seller? Why does the forum have to play a part in how they negotiate? I’ve had people ask me to ship using a cheaper method. I agreed and charged them less for the total sale.
There are legitimate gripes about finding out about shipping fees after the fact. That’s obviously lame and not recommended. But, if the buyer and seller have clear communication, their transaction should go fine.