First off, let’s make sure that we’re distinguishing between bots and what’s being purchased from the AH.
First off, Bot are banned by the thousands and it’s done daily. There’s a sticky thread in the Classic General forums that outlines just some of the actions that were taken at the time of the post.
As for people who pay real life money for illicit gold, those accounts are also often flagged once the botting account is identified. Then they come to this forum or third-party sites and explain just how “innocent” they are and how they didn’t do anything wrong!!
If you see someone cheating, please be sure to right-click and report them as such. There won’t be a lightening bolt from the sky that bans them, but the report will indeed be looked into.