Those cheap licenses are always used. They exploit the fact that these can be used to activate ~10 copies of Windows. It's even worse than that though. One sell

Those cheap licenses are always used. They exploit the fact that these can be used to activate ~10 copies of Windows. It's even worse than that though. One seller could keep track of this limit, but what happens is that a bunch of sellers source their keys from other similar sellers. So they don't even know how many times a key has been used. Last time I bought one of these 15€ keys for a friend, I had to write to the customer support over 10 times and shuffle through at least 6 different keys until one actually worked.