i usually do this method of investigation:
1- look at the feedback of the seller if there's someone with (978) feedback on previous deals.
2- look how many bids he's doing, maybe there's something from another seller close to the end, then do as point one.
3- look for similar items, same casino, same denomination, same theme, on the completed listing only, if there's someone with the same feedback.
4- go random, look over items on sale, with (978) feedback he's almost sure he's a seller, so you can look for a seller with (978).
5- go extra random, look over all the completed listings to see some seller/bidder with (978) feedback.

LoL i have time to lose, i know...

"Special Agent" Mauro