Ruse with Sutherland? **Spoilers, perhaps**

Yes. It's illegal for an auctioneer to partake in his own auctions, because that would be similar to why Martha Stewart went to jail. Having insider information in order to get things at cheaper prices (and to an extent, even controlling the prices himself based on what artists were deemed popular according to his expert say-so). So Virgil knew what he had ahead of time, what things were worth, and he was getting paintings he wanted by ensuring that other bidders never even had a chance because Billy would big higher no matter what.

On top of that, Billy was a talented reproduction artist (he makes a comment to Virgil about how he never appreciated him as a real artist - "I was good enough to make your fakes for you" but not good enough to be considered an artist in his own right), and it seemed like they had also been involved in auctioning off fakes while Virgil kept the real originals, in the past.

Since Virgil was such a well-informed expert on paintings, even other experts took his word for it when he said something was genuine or not, and he was often passing on bad information to hide the fact that he had his own private little museum full of expensive art. He was lending credibility to fakes as well as declaring genuine paintings as fakes in order for him to buy them cheaply and then resell later as the genuine article. That's why he flies off the handle when Bills gets slack and misses the bid on the painting that went for 20 thousand. Billy says "it was just a reproduction" and Virgil said, yeah, that's what I told them, but it's actually the real deal and worth 8 million. So Billy is not only bidding for Virgil, but Virgil's got that entire corner of the art world under his thumb and he's not just collecting the best for himself but bilking all kinds of customers out of millions of dollars, and passing on bad information & lies as well.