As an occasional ebay seller, this is the problem I have.
I've been stung and had to eat extra shipping before
I just had a cluster with the UPS and Paypal shipping sites.
UPS stonewalled me.
Finally got it resolved with the Paypal rep. But still had to pay extra because my account was dormant and there was a lag in the "discount".
There probably are ways in knowing how to not let that happen if one is savvy with the system.
But I just use caution. I'm not going to eat shipping to China.