Hey Leslie Anne! Good to see you on here again. I don't think there's anything wrong with selling glassware, shirts etc on ebay, any more than there would be if you opened up Leslie Anne's Greek store down the street. Alum directories are a little more dicey, but I cannot imagine a non-member would want one - talk about boring reading!
To me these things are "public" - you could go to a physical store and buy them, and even our magazines are open (NPC gets a copy of everyone's mag). The only things I don't like seeing sold on ebay are "private" things that only members should have access to, like pins and pledge manuals.
OK accountants in the house - say Leslie Anne buys a Mu Mu Mu badge at an estate sale, and MMM nationals doesn't have a program like DZ where they could reimburse her. If she gives this back to them, could she write it off on her taxes as a charitable donation?
Now the lawyers - can a national put a clause in its bylaws to the effect of "The official Mu Mu Mu badge may only be possessed by a member, any sale or gift to a nonmember will result in prosecution"? Of course this would only work if it was enforced. For some reason I seem to remember hearing about a ring of people selling Phi Beta Kappa keys and getting in mucho trouble (this was before ebay).