I think you are being a bit too charitable. If you send something which is being traded into and out of currency on behalf of someone else, or on your own behalf, you are have to ask the question if this is legitimate or not.

Now if you sell PEZ collectibles on Ebay for others, and find they start sending you back the same collectable you sold before, you have to sit back and ask, Hmm what is really going on here? And if you don't do that, then you risk finding yourself, like Shrem did, in a place which really wasn't a legal place to be. The key here was the judges observation, "months and months" of activity. If you do this and stop for a second and say "Hmm, why is this so profitable for me, what is the deal here?" a couple of weeks in, maybe even a month in, and you document seeking legal advice. Then you get off with a wrist slap. It was like the bitcoin for gift cards site that someone here said was "amazingly profitable", you have to stop and ask yourself where is the "value" here that I'm getting to keep so much of it.