Hi S.F.
An account set up and left dormant, they can be sold or given to sellers to up their listing prices / feedback rating.
For example I recently bid on an item, the starting price was 99p. I put in a maximum bid as I didn't expect to get it for this, however, as the listing came to an end it was still at 99p, then I was outbid. Nothing strange in that so I bid again and won. I then looked at the other bidders details and found the account was opened over a year ago and they'd never won anything, this raised my curiosity.
I then looked through this sellers previous listings and found 25 of these accounts all of which are anything up to 1? years old (each used several times)with no items won or sold and no feedback, they are always used to bring the original bidders bid up to their maximum bid, I suppose if the bidder doesn't bid again the seller can say the other (ghost) bidder fell through and offer you the item on a second chance obviously at your last bid which is now your maximum bid.
This guy is a power seller with over 10,000 sales, imagine how many they've done this to as I only looked back less than a month.
I should say this is all my own opinion but as I said it looks a bit dodgy.
I'm now unsure as to what I should do, As I've paid for the item before noticing anything weird.