TL;DR I would not recommend going with TanTan in the future, and do not count on PayPal purchase protection to save you. Lessons learned...
Well, after much back and forth, we were unable to come to an agreement on shipping.
I was prepared to eat the shipping cost until I found out an unpleasant truth, it's much more expensive to ship things from the US west coast to China than the other way around! The US Post Office refused to take the package due to the size, and UPS, Fedex, etc. were going to charge upwards of $800USD! The cheapest I could find was BikeFlights at ~$300 USD, but at that rate I might as well just get it repaired locally and not risk further shipping damage.
Unfortunately PayPal Purchase Protection wasn't much help either. In the end, PayPal agreed to refund the total cost of the frame if I returned it, but with the aforementioned cost of shipping, that's a non-option for me.
Looks like I will be going the way of local / home repair, which I'm fine with. The damaged area doesn't seem too large or located in a critical structural area, so I imagine a repaired frame will be okay, I just would have preferred not to take the risk or eat into my slim budget...
On the bright side, at least I can proceed with the rest of my build! I'm pretty excited, as this will be my first full-sus bike
I'm genuinely curious, does anyone have experience with shipping bike frames back to China at a reasonable price?