I just started listing a few things myself, which has me paying more attention lately to eBay listings.
A *lot* of weird stuff: Clearly worn coins being touted as "proof," absurdly high prices, etc.
I have some thoughts, some plausible some tin-foilish.
Absurdly high Buy-It-Now with "Make an Offer" can be directed towards a particular person (ask me how I know... no, on second thought, don't). The seller is a newbie and couldn't figure out how to make a one-person auction.
Money laundering (which could explain the bidders on clearly overpriced junk).
People's children listing with their mommy or daddy for fun.
People with a weird sense of humor. Utter ignorance. Whack jobs. The information-uploadedly challenged (what we used to call mentally deficient, but I bet that's impolite these days).
Any other ideas?