Bots are illegal in-game for the following:
- Fighting for the user, because it's unfair the user doesn't have to work to get Qi
- Advertising Servers
Bots are legal on the forum for the following:
- Updating prices and auto-buying, because it's fair the user doesn't have to work to keep on top of the market, because after all he spent "so much time" making the bot, he should be able to use it.
- Spamming items onto the market, as well as constantly changing
It's stupid how bots are allowed on the forum for the exact reasons why they aren't allowed in-game.
I could be wrong, but Thrandir was probably M-squad during voting process for legality of bots, no coincidence if he said yes and now is one of the more advantageous bot users.