You're absolutely right. Over the years it seems that eBay has been diligent in removing this type of listing, as it does promote the selling of knockoffs and using real COACH dustbags for the merchandise.And by wrong I mean it is actually prohibited by ebay. If spotted the auction will be removed.
I keep mine and use them. Some of them I set aside for use with gifts later. I've purchased mini skinnys from Macy's/Dillards and they've only provided tissues and boxes, not dustbags.
From what I heard, it is now prohibited to sell dustbags on ebay (one of the reasons is as what mrscook posted above). Not sure if this listing will be considered against the policy since it includes other items.