Well, I used to accept only US customers, but
have changed my auctions to allow international
customers... *but* there are limitations...

I think the biggest problem for US eBayers is
payment.  I know my bank charges a hefty fee to
cash international money orders ($27 plus a 
percentage/"collection fee"!!!!), but the post
office will cash international POSTAL money
orders.  The problem is, some countries can't
get these types (or they take a really, really
long time).

Luckily, with Paypal accepting a lot of foreign
countries now, payment can be received that
way (for most foreign customers).  Plus,
BidPay (ugh, I don't like them, but they are
an option) will work with some other countries.
So, the payment options for accepting foreign
customers for US sellers is a little better than
it was before...

However, shipping presents another problem.
It's almost impossible to give a shipping cost
for a country when someone asks "if I buy, how
much will it cost to ship here?"  You almost
always have to make an extra trip to the post 
office with the package to ask for a quote... and
if the international bidder writes with less than
a day before the auction ends...?  Ugh.  Plus,
shipping to some countries (even a smaller 
cd-size package) with insurance and/or some
form of tracking can get expensive, and it gets
frustrating to have to try to "justify" the USPS
rates to someone wanting to buy a $10 eBay item.

If a seller says he/she won't ship 
internationally, you can always ask to be an
exception.  I can understand, though, why many
sellers wouldn't want to take on the extra hassle
and frustration of international payments and
shipping (although I have met some very, very
nice people from other countries simply as 
a seller or customer through eBay).  =)

Kim ^.^
aka Lady Zatara