Well, I know for one it was illegal to sell points in Arenas in WoW. It could fall under your 'mercenary' category. I am impartial to either way. I used to sell points in WoW Arenas for people who wanted to get ahead or were making new characters but didn't want to grind out the gear. It's considered throwing matches and whatnot and exchanging wins.

As far as selling spots, we sold gear to people but required a deposit up front. I assume that's the same thing you do. I don't plan to be doing this anytime soon as I think it ruins the experience personally, but there is not enough GIL circulating right now through NPC's and other things to really justify taking money out of the economy as it currently is not a really effective way to generate revenue as it is just recirculating and changing hands, eventually going away (into repairs).