I had a recent small problem - I sold a reasonably heavy item (4kg) and in the listing warned that shipping outside the UK would be expensive. the buyer was in Italy and I quoted the cheapest airmail I could find, £25 ($50). The buyer replied "is this a joke? I buy from UK all the time". I replied with the weight and dimensions and said that as the listing said, I would only be charging them the actual cost and if they can find a cheaper service, or ship on an account I would be ok.
We eventually agreed to cancel the sale, which I am happy about, firstly because it went for a lot less than I was hoping, and secondly I would be very wary about shipping my item to a reluctant/complaining buyer.
Gareth