I have only really ever had issues as a buyer from German sellers believe it or not, namely just plain old ignoring your emails saying it doesn't work!
I find the most accommodating, once you get past the language barrier are the Chinese, although it takes 3 - 6 weeks for the items to arrive if they arrive damaged or not at all, they usually ask for a photo over the most obscure things?! But always in my experience rectify the issue at their cost almost immediately, you just have to wait for it another 3 - 6 weeks! Bloody Hong Kong post.
UK sellers are hit or miss, I have had one item from Poland and it worked out fine.
The thing with Chinese sellers, even though they might have thousands if not more positive feedback responses, one negative hurts them and their shop, to the point where they literally beg you not to leave negative feedback.
To be honest, I have never left negative feedback for any Chinese seller and will always give a chance for people to redeem themselves as it were, but I guess some people are trigger happy and that is what they worry about.
So if you ever have an issue with a Chinese seller, threaten them with negative feedback (don't actually leave it unless you really have to) and 99% of the time they will sort it out, but as I say, most cases you don't need to threaten, they are quite reasonable sellers and actually seem to care what you think of them and their shops! Novel eh!