1. Everyone wants to think that auctions are rigged and that the seller has shill bidders arranged by the seller or that the auction house is "in on it". Yet after two decades of watching Barrett Jackson and Mecum on cars that went for screwy money (either high or low) there has been no proof of those allegations. People are absolutely the worst secret keepers. If such collusion were really happening you'd have heard about it by now. There are a few "a friend of a cousin that knows someone that saw the auction is absolutely positive that George and Sam ran up the bid" but in no circumstance has an individual supposedly directly involved ever admitted it. So this remains an old wives tale.
The only auction shenanigans I am aware of happened at Barrett Jackson when someone was selling a Bugatti Veyron. The final bidder got the car for an absurdly low price. I was in Craig's sky box when having not been on the podium at the time came on and said that the bidder "lied" - he didn't have the money, was caught in the moment, and figured he'd get outbidded and was summarily evicted for life. Craig re-opened the auction with the previous bidder having first dibs but he rejected resuming the bidding and Craig ended up buying the car personally for the shill's bid. It still shows up at the Scottsdale auction with a BJ wrap on it - it's a "company car" and written off
2. Eleanors get screwy money. Just look at the last few that went at Barrett Jackson (I think there were 3 or 4). Now that they are "legitimate" (business wise, of course they're a copy of nothing) the reluctance to put them out there is gone and they still get top dollar. There's no logic behind it except that they are cool looking.
3. According to the feds capital gains ARE due on profit of auto sales (as they are due on art works - if you find a rare bowl for $5 at a garage sale and sell it for $5M, you owe capital gains.) Sell a car for a profit, you owe capital gains (but they depreciate like a rock and you don't get a deduction, unless you're a business.) Maybe some of Biden's 80,000 armed investigators can track down some and audit them.