Just to point out, creature trades have also probably been conducted for years via this "middle-man" method, Ary.. its definitely not limited to RP items and it didn't start now. Are you gonna go back and undo all those now?
I definitely agree with Z, its not something that can be called a direct abuse as such, its just a clever workaround and its something that's difficult to prevent (just like in RL, there are always crimes that you can't prevent). On the other hand, its also a risk because if someone who spends enough time and effort to check logs for such cases catches you and has evidence, you can get into trouble (again, like in RL, you have to try and make an effort to prevent a stealthy crime, its not all automated). So yeah: you _have_ the ability to prevent these middle-man trades, but you're too lazy to make an effort to do it and blame the system as usual. Stop complaining, make it fun in some way, turn this into a role, whatever!
(The above is meant to be encouraging, not degrading. Its kind of obvious that if you want to prevent "middle-man" trades through coding or automated method, a _lot_ of trading will become restricted and it might cause major problems later on, eg: I award Azrafar a silver coin for a quest and two years later he buys a creature from my alt and happens to give back the same silver coin...)