Earlier quoted context omitted.
Until you discover it's an illegally sold volume license copy and the volume license gets voided. Fun times, fun times.
Does this still happen? I bought my Win10 Pro key from a grey market site for like $10, so I figure it's likely an illegally sold volume license copy. Yeah, I totally acknowledge that it could get voided, but I know several other people who have bought their Windows key from these types of sites, and none have ever had a problem.
As a customer, the question of the legality of the license key is not my concern.
I purchased it, Microsoft checked it, while knowing my IP address, and decided it was good to go. The fault is theirs: if they don't want volume keys to work outside some markets, add some limitation like geolocalization.