Just to point out the other side of the coin.
I will argue that not all cases of main vs alt item trades should be considered alt abuse.
The easiest example is if the alt had earned the item one way or another, either by requesting the item to be made (which includes getting the needed wishpoints, materials etc), won it in a quest/contest, or got it for good RP from Mur/others capable (Tengri made a lot, IIRC. This doesn't include me, btw, cause I can't gift people with items - I take their wishpoint in the process). Even though they didn't earn it on their main, they stil earned it and it should be, IMO, their right to do whatever they wish with it. If, for example, Keith had commissioned an item, don't you think it he should be allowed to give it to Tarquinus (or sell it for a creature to be given to Tarq) at will? -Sorry for using your name here Tarq, just thought you'd make a good example-
While I understand this is not the kind of case you are concerned about and far from the reason the topic was created, I feel I should write this to prevent public opinion from being skewed towards "[b]all[/b] item trades from alt to give something to main" is abuse.