It's not easy to descry if this is the case. But what you could do is to check the seller's auctions. If you see this guy with 31 feedback bidding on many items, taking the bid back or something else it could be the case that the seller has 2 accounts or someone who bids on his auctions.
I thought it was weird because the other guy took his bid 2 times back.
When I was younger I used to push my own auctions that's why I maybe thought that this is weird.
But as long as you are happy everything is cool :)