Adding paypal fees isn't against ebay rules, it's against paypal rules. If you consider Paypal a type of Credit Card, then charging a surchage is against California and US law.
I see it all the time on Ebay (yes, I said Ebay) and it starts to tick me off for no particular reason...
The way the system works (with seller receiving payment first), it seems there's not much risk to the seller short of having your time wasted.
If your buyer doesn't pay, well, just forget about it and relist already...jeez, no need to be petty.
I've ran into plenty of idiots on Ebay and none of them are worth this kind of time and effort to get them.