I am not a mod on this site, but it is my opinion we already have too many "rules" in regards to the buy/sell section here.
I expect though, that since this site is only a way to connect sellers with buyers, that they hold no liability towards how that transaction is completed, since that is done completely outside of this site.
also, its my opinion that those types of details should be only between the buyer and seller. if someone suggest that you as the purchaser must also cover the fees, its up to you to make a choice whether you want to continue with the transaction, or not. or at the least, take some control of the situation, and talk to them about the fees about whether it is negotiable or not.
lastly, if you run the transaction through paypal as a gift/family, there are no fees. this then, becomes a non-issue.