There are plenty of flippers out there who are complete scum bags, so it wouldn't surprise me if situations like that are examples of shill bidding. I've been $1,000 (FMV) books on ComicLink priced at, say, $5,000 with $4,000 bids. I just think, "Dude, no one is stupid enough to believe that you actually got a $4,000 bid on that $1,000 book."
Of course, the seller is hoping will someone who hasn't done his homework will see the books and think, "Duh . . . someone else was willing to pay $4,000, and the seller didn't accept, so the book must be worth more than that."
There are quite a few con artists out there, unfortunately. Some of these dirt bags will take two copies of a $100 (FMV) book, price one at $200, and price the other one at $400. They're hoping that a gullible buyer will see the copy priced at $400 and think that he's getting a deal on the one priced at $200. It takes a certain amount of diligence to avoid being conned by these grifters.