Affiliate Marketing Secrets

I see a lot of advertisements for the Diablo 2 item vending sites that sell runes, characters, cd-keys and such. How do these sites operate and are the affiliated with Blizzard in any way? I heard blizzard allows these sites to operate and conduct their business on battle.net servers as a way of passive income. But, what I want to know is how they actually operate. Where they get their items from, the characters and the cd-keys. Are they legit? I’d like some actual info not some retard going “I THINK DEY IS GEWD. THATS A FUN GAME.”