I am duly chastised.
Thank you, Shopaholic for your thoughtful post. It sounds like an account takeover to me, too, now that I know such things exist!
I am surprised that ebay/paypal hasn't contacted me to explain that they negated my order. It just disappeared! The paypal charge never went through to the seller, but I had to go in to my paypal account to cancel it.
Meanwhile, we bought a refubished Kindle Keyboard for my husband through Amazon Warehouse. I dragged him to Best Buy to look at the models they had on display (all but the DX). We took his old Kindle to compare, which helped him decide that the Pearl screen was a real upgrade -- he knew he wanted wi-fi, hadn't known he cared about screen quality.

It's too bad he won't have the larger DX, but I think he will love his new KK!!
Thanks to everyone who weighed in on the ebay sale question. I learned a few things.