No, this is why systems that aren’t rigorously designed to preclude exploitation like this simply shouldn’t be released. If flaws like this exist in the system, they will be exploited. It’s not on the users if they exploited a flaw, even if you say “please don’t exploit the flaw”.

Microsoft Rewards isn't a "nice thing".

They're giving out made up points and then letting you trade them for copies of digital files. They're not really losing much.

If you actually started selling these, they would probably shut that down pretty quickly and maybe even sue you