I recently integrated paypal. I did a test to see how much extra we could charge if the customer chose an obscure shipping address and there didn't appear to be any limits like I was expecting(I was expecting a percentage +- of the "confirmed" amount).

I asked paypal and they confirmed that there's no limit.

It is a little weird, but since paypal always sides with customers in disputes, it's probably not so bad if you get hit with this.