I think your rules are very much within reason and
they really can't do anything about it, that's the
whole reason they are throwing a fit.  You have
the right to refuse to sell to anyone for any
reason and you also can choose your shipping and
payment methods.

Even if they have an American friend to bid on it
for them they are still going to end up paying the
same for shipping because it's going to have to be
shipped twice.  If you shipped another way you
would also have to include the packaging cost
which would probably make it about the same anyway..

I also ship the same way, if they don't like it
that's tough.  I want to be able to protect the
buyer as well as myself.  I say, the few extra
dollars is worth the piece of mind..

Honestly, I don't see why it's worth complaining
over a few dollars more?!