Players are free to advertise services (dungeon runs, powerleveling, etc.), but these arrangements are undertaken at the player's risk. We have no ability to investigate trades outside of the in-game trade system, so these are the only exchanges we are in a position to enforce.
Perpetrators of trade scams may be subject to disciplinary action and will have their posts removed, but unfortunately we can't guarantee our ability to retrieve items lost to scams, so be careful. If an offer seems too good to be true, then it probably is.