OP said "it was literally impossible to buy a computer with a legal copy of windows installed on it".
Responder said "it is quite possible (even common) to buy a computer with a legal copy of windows installed on it" and asked "is a Windows sticker on a laptop good proof for legally installed Windows?" with the assumption that pirated Windows does not come with a sticker.
PS: That assumption turns out to be debatable [0].
In Asia most brands sell the laptops without OS for cheaper price compared to the same model but with windows preinstalled. Some stores may install a bootleg version for free or even fake it as a genuine Windows install.
Responder said "it is quite possible (even common) to buy a computer with a legal copy of windows installed on it" and asked "is a Windows sticker on a laptop good proof for legally installed Windows?" with the assumption that pirated Windows does not come with a sticker.
PS: That assumption turns out to be debatable [0].
[0]: https://item.taobao.com/item.htm?spm=a21m2.8232368.0.0.TlUMn...