How can I monetize ethics?
We live in a society. We try to abide by the mores.
They'll also absolutely sell it to China, they'll just be quiet about it and use one of many Thailand-based intermediaries.
The companies that immoral & legal, have paved their own way, but since you're not going to be selling to governments directly, don't count on being able to get away with it.
I guess far bigger problem for researcher would be to actually not being scammed while selling and this is why companies like Zerodium have their marketshare.
Yeah someone could pay to you in crypto, but chances that you'll just gonna be scammed are extremely high.
There might not be a high profile "this dude sold a 0day and got arrested" case yet, but there are cases of folks selling software / hardware cracking tools getting indicted.
There's also this really interesting story:
https://www.wired.com/2013/03/alfred-anaya/
Dude caught serious prison time just for making hidden compartments in cars and they put him away based on the fact that he knew his customers where in the drug business.
Selling high impact 0days definitely seems like a risky business IMO.