This is false. A pirated Windows 10 Pro license costs like $25. These are not legitimate licenses, they're overprovisioned enterprise keys being sold in violation of the license agreement. And yes, they register differently in Windows, and can be easily detected. (Command is slmgr /dli)
Like, if you want to pirate software, go pirate software. If you're going to pay someone on a per-install basis for pirated keys, I'm gonna laugh at how easily you're being taken advantage of.