It’s one thing to run a friend through a dungeon that might be a little too rough for them because you’re a Cool Pal. It’s something else entirely to do it for a rando and ask for real money in return. In World of Warcraft, the latter is unacceptable, and Blizzard’s started banning top players for it.
Source: Kotaku – Blizzard Bans Top World Of Warcraft Players For Trading Dungeon Runs For Cash