I see shills drive people up to their maximums all the time. If they go too far, they just retract their last bid. I'm not suggesting that happened in these auctions, as I have no idea - but it's certainly not uncommon.

I didn't participate in the Yee auctions, but for the heck of it I just pulled up the eBay history on the top-selling Ruth/Gehrig photo. It appears only 2 bidders bid more than $495. It looks like the winner was top bidder at $500 with a few hours left in the auction, then someone put in 12 consecutive bids in $100-$300 increments in just 8 minutes, driving the winning bidder up to $3750. That could have been someone's perfectly legitimate approach to bidding - they could have kept telling themselves they could afford to go just a couple hundred bucks more, just a couple hundred more, gotta win, gotta win - but it's also what shilling consignors do. Keep bidding in small increments until the other bidder's max or near-max is exposed, then retract if you go past it, or don't pay if you accidently win; or drive the price up to what you're comfortable buying the piece back for and try again later.

Whichever kind of bidder this was, this situation is why I never put in a max bid until seconds before an auction close.