I dont understand the art world but I do know that the art is sold by the auction house for a commission and the owner of the art has to be paid. So if Billy wins the auction he is supposed to pay the auction house which takes the commission and pays the rest to the owner of the art. So I dont understand the scam or if there is an illegal activity at all. It just does not make sense. Its a big plot hole. I dont understand why none of the other viewers did not question this.
Oldman indicates to Billy the piece(s) of art he wants. Billy makes the bids. Oldman slights other bidders and/or rushes to the gavel to end the bidding to ensure Billy wins the bid. Billy pays for the painting out of an account set up for this.
So Oldman gets the painting relatively cheap, gets paid for his services, pays Billy handsomely for their scam and no one is the wiser.
I don’t need you to tell me how good my coffee is.. .
The previous poster laid it out pretty well. Virgil also deliberately misrepresents the pieces as less valuable than they are, such as the copy that wasn't a copy, so that he can afford them. He obviously is very rich in his own right, but not at the level where he can just write a check for eight million every time he runs across something extrardinary. Plus he enjoys the game, the win.
Billy does it for money, which Virgil pays him. Virgil just wants the art. There's no profit financially, for Virgil, but the original owners are being defrauded of millions.
It's a pretty despicable crime. These things ought to be in museums (and IRL, the pieces used for the film mostly are), not locked away for one man's selfish pleasure. Then there's the loss to the owners of money they rightfully should have had. They are usually quite rich themselves and will not be hurting as a result, but he's still stealing from them. And they may not all be rich either.
It's entirely possible this kind of thing happens in the art world all the time. Who would know? Sometimes even the world's leading experts can't agree on whether or not a piece was done by a particular artist.
"Oh, dear. Mr. Dictionary seems to have deserted us again."
These pieces would not have ended up in a museum, but in someone's private collection. Although a legitimate owner would be more likely to allow a museum to display them periodically.