This is usually when I resort to VISA + purchase insurance.
Is the seller refusing to take the unit back in violation of their return policy? Or is the buyer refusing to abide by the terms of sale they agreed to when purchasing the unit (i.e. demanding return shipping to a foreign company be seller-paid when it's specifically disclaimed in their ToS)?
Credit card chargebacks are for the former situation, reading things you agree to before you agree to them is for the latter.
Actually that's between the vendor and the credit card company to be honest as you only pay the credit card company for their services at the end of the month.
Also if you ship something internationally it's a rat's nest of import/export duty, local laws, consumer laws, national laws, foreign policy and utter unadulterated pain that is worth abstracting through a card company. If you get a lemon, let them deal with it - that's an official service they offer.
It doesn't usually result in a chargeback, just a UPS pick up at your door. You only see chargebacks for small items that aren't worth arguing over. That's a known and planned cost of doing business via credit cards.
(Note: I was a technical architect at a rather large well known European credit card company so I know this stuff inside out)