Here's the rule-of-thumb, these small time sellers are interested in sales, not pwning you. They may counterfeit but they aren't going to bother installing backdoors nor are they sophisticated enough to do so. They may inadvertently do so out of incompetence but that was not their goal.
People who really do want to pwn you wear suits and sit in large offices and they will get you to do it voluntarily by signing a EULA.
You don't need NSA cash, you just need a place that will pay your X dollars to put in their advertising / monitoring malware on the device. The reincarnation of the browser bar.
Good luck doing that in China. It is provably the best and quickest way to end up in an unmarked grave or a secret prison and doom your family at the same time.
People so often rationalize away a plausible scenario of government surveillance by showing how it would require someone to be an irrational actor -- under a simplified, incomplete set of assumptions about the world. I do not understand why, after Snowden. Humans are not rational, and you cannot exhaustively list all the possible forces that might affect someone's decision.
The manufacturers may be based in China, but the importers, distributors, and sellers here discussed are not necessarily so. And I suspect you could happily replace NSA in the parent comment with any private or government intelligence agency of your choice. I wouldn't expect an unscrupulous distributor to suddenly grow scruples about precisely where the cash comes from.
People who really do want to pwn you wear suits and sit in large offices and they will get you to do it voluntarily by signing a EULA.