Chozo, 2 lata temu

It's pretty common for online games that have player-to-player trading systems. The developers are usually very protective of their in-game economies, because while they don't officially support grey markets, they know that the existence of grey markets is the sole reason a huge chunk of players (often whales) play their game in the first place. It's in Blizzard's best interest to ensure that there isn't in-game inflation.