The reason GAF doesn't have them is because they are more trouble than they are worth.
Even if you put up a notice that the mods/forum has NOTHING TO DO with the trades, the mods will get pissed really quick once someone gets scammed or someone doesn't send shit out, and they have to deal with the fallout of a poster telling them they HAVE to do something.
Yes, they wouldn't have to do anything, but this community is small, and they would probably feel compelled to try to do something.