If you are just buying things, you can use your US eBay account to buy, and then pay with China's PayPal. In fact, as long as you are buying things, you can use anyone's PayPal to pay, as long as they are willing to let you use it. I have a classmate in Australia who uses his own eBay account to buy things, and I often use my PayPal to pay him, no problem.

But if you are selling things, the situation is completely different. First of all, your eBay account cannot pass the seller qualification certification (because of false information), and you cannot provide valid proof of eBay's registered address, so you can't become a cross-border seller at all. Moreover, as long as eBay or PayPal finds out that there is any false behavior, just in case, they often block the account first and require you to provide relevant supporting documents, otherwise it will be frozen.

In short, if you are a buyer who is purely buying things, the situation you described is completely fine.

PS, uncertified US accounts are also easily blocked in China. I once asked my Australian classmate to help me apply for an eBay account in Australia, using another classmate's information. As a result, I was blocked after logging in a few times in China. I guess this has something to do with the IP. However, this situation will not happen with certified accounts. The accounts in my company are all eBay accounts registered in the United States, but we operate in China.

No matter where you register on eBay, the mailing address can be changed. You only need to add a new address if you want to mail it to a certain place. You can also send an email to the seller to explain it after payment.