I always ask the buyer to pay the fees. The buyer has the option of sending the money as a "gift" in order to avoid the PayPal fees.I've also started using a new service from http://www.Venmo.com Functions very similar to PayPal but has a "social network" feel to it. Many of my friends use it. It has similar fees as well except if you use a Debit card, there is no fee. Not sure if PayPal does the same for debit cards.
While they can use the "gift" option to send the money, there is still a fee unless they pay from a bank account. The fee still applies if they pay by credit card. And many people want to pay by credit card. I think in most cases the buyer would be responsible for the fees. Though always negotiable. They can avoid the fee by paying by bank withdrawal through PayPal.