Perhaps you could do what I just had to do.

A buyer could not purchase multiple without paying for each individually.

Went to bulk edit - changed all including COD Pick Up etc.

Could you do same with Postage - cut out all international postage on all your items if you do not post anywhere but here.

Seems sometimes the eBay pixie ( & I'm sure there is a number ) gets in there with it's little wand and does some very strange things.