An anecdotal story: I bought some Windows 10 keys a few years ago from a site pcmag "recommended," where they were selling Windows 10 keys for maybe $55 each. I bought two at the time. I kept the keys saved in my email. Fast forward to last November during a minipc build, I planned on using one of those keys. I tried it. It was rejected as a non-genuine key. I thought being written up on pcmag was a recommendation, but it was probably not a vetted source beyond being cheap. I learned my lesson and I will buy through Microsoft or through Microcenter (us brick and mortar store).