You're not the first AW author to notice his ARC available for sale
before the book is available for sale. It happened with "Obedience" before it came out about a year ago (Will Lavender posted about it back then but I can't find the thread offhand - looks like he hasn't been active, either here on on the blog on his site, in many months, hope he's doing okay). It seems to be a common occurrence.
I think it might well be illegal to sell BEFORE the book is released. I agree with Susan, ask your publisher what they think, though they may not be too bothered by it as they may have bigger fish to fry.
After the book is published there's the "First Sale Doctrine," a legal ruling that (as best as I recall, perhaps you should look it up) since the text is already for sale, ARCs and uncorrected proofs can then be legally sold, regardless of any "not for sale" stamp on it.
Many online venues such as Amazon do not allow ARCs at all to be sold by used booksellers, even if the book is decades old, apparently because it's easier for them to disallow them all. And from what I recall of the news stories at the time, Amazon may have been responding to pressures from publishers who were complaining about losing new-book sales to ARCs offered for sale online.
You can complain to eBay, but to be effective you have to go through whatever process it is (I forget the name of it now, they might have changed it anyway) to register as an IP/Copyright holder, then all you have to do is send a complaint about an item for sale, and they'll take it down (from what I saw a few years ago they don't even double-check the validity of your complaint once you're registered with them).
ETA: I just looked, it's call VeRO for Verified Rights Owners. If you have your publisher sign up here, I'm pretty sure they could have this auction brought down (whether it's actually illegal or not):
http://pages.ebay.com/help/community/vero-aboutme.html