Sadly, I feel that so far, the only answer of any real worth, is the one from "apple_tech" (answer 10).
Personal anecdotes, really awful suggestions, and condescending answers (which are really quite insulting) only muddy the waters. It would be good if somehow "the Community" could hive off the less helpful ones so that people searching for help could get their answer quickly.
Re: Import Tax and Duty, It is not a VERY complicated subject for singly items, but it is easy to fall foul of it through lack of knowledge. The crucial point is then when HMRC identifies goods as liable, then the person importing (not the seller) is responsible.
Although the listing can warn of possible taxes etc. by virtue of the "location" information (which is all too easy to miss), rather than many people finding out the hard way once, it would be good if, before a bid or BIN price is accepted on the system, a warning was brought up to make sure the user understands the potential liability (relatively easily coded when the Buyer location and Item location are different countries).
Not Ebay's "fault", certainly, but having facilitated inter-continental purchasing (from which it profits), it would be good for just a little more hand-holding for the uninitiated.
I think this is important because through such purchases, Ebay makes money, the Seller gets their money, and the inadvertent buyer then doesn't get the great bargain they originally envisaged but cannot afford to just abandon their purchase.