There's always going to be an element of risk because the most legitimate brands and sellers are preoccupied with selling to the Chinese domestic market rather than chasing international customers. The domestic brands popular in China are unheard of in overseas forums. Likewise, nobody rides Velobuild frames or Elite wheels in China.
This is to say that you really need to do your homework when choosing who to buy from. If you need the most thorough support then you're stuck with the most established brands. I also steer clear from first batch products because the game plan for most small companies is to rapidly iterate and issue warranty replacements to early adopters - something easy to do within China where shipping is fast and subsidised but practically impossible outside.
If I want the most thorough support, I'm going to my local bike store where I know the owner, manager, bike tech, and the sales staff from all the business I've been giving them for the past 2.5 years. I've had everything from lights to entire bike frames replaced or exchanged, FOC, no questions asked, mostly right on the spot at my lbs. Heck, most of the service calls I've done with them have been FOC, even on my Chinese bike. Most of the stuff I buy, dollar for dollar in the long run, would be a better value through my lbs
. Their issue is that they are just limited as to what they can carry on hand and what they can order. Believe me, if I were in the market for a $9,000+ bike, I'd get it through my lbs if they carried or could get it. Sounds like the Chinese in China recognize this too.
EVERYTHING else...Chinese sellers, EBAY sellers, any online seller...has been a crapshoot. As with the vast majority of sellers, most transactions, thankfully, are issue free. Support isn't just about what happens if there is an issue, though. It's getting you your stuff, in a reasonable amount of time, damage free, and communicating with you when you reach out and Chinese sellers don't stand out either way.
But yeah, do your research. I have my list of sellers and will rarely step outside of that list.