The problem is that the objects (albeit some are honest and true) are not always exactly as listed. For example, I can take a picture of the BRS CD, and notes from the internet (which will look new), sit down on CD stamper and pump out 1000 copies to sell "brand new" on ebay. I think that the problem lies in that people (dishonest) will market something alike what was noted above "brand new, unused, in the box books" when in all reality, they are brand new, but have been published elsewhere (offshore), and have circumvented the royalty fee.
Kaplan, Ebay, and obviously nobody else can verify that these goods are indeed original kaplan material, and they end up losing their $. What if boils down to is that Kaplan (and others) can file a suit against ebay for marketing these items, so ebay will pull the entire list, instead of trying to determine which items are legit, and which are not. The same thing happens w/CD's, comp programs etc. as well as other aspects of our market (pawn shops,who do have to verify their goods)
Don't get me wrong, I hate the fact that we can't sell our books (I too have a set I want to sell), but what you can do is sell them at school, online at other sites, or possibly here on SDN. Also, when you sign up for Kaplan (I could be wrong) but read the fine print that the material is non-transferrable, as I know that we all signed the dotted line/check box after the huge page of legalities.
As far as a Kaplan monopoly, yes they do have one in this area, but there are plenty of other choices as well, some better (BRS), some upcoming (USMLEasy), and others that should jump into the market (princton?). It is a free market.
sorry, I am not super pro kaplan and am not affiliated w/them, I just think that people are trying to sugarcoat what is basically theft, which is now starting to hurt our ability to sell goods.