It sounds dangerously close to obtaining, or attempting to obtain, money, by deception; the bidder is subject to the dishonest false representation that there is someone else who is wants to buy at the given price. The difficulty is that the house that opens bidding by suggesting a figure, which they all do,is inviting a bid at that price yet nobody has offered it.Nobody could reasonably complain about that. Anyone who bids at it might be the only person in the world who would take the price. It is difficult to distinguish between the two situations.
In addition,with art and and antiques, the major auction houses have a term that the house may bid up any lot in which they have an interest. The interest is not specified, but may be that they have advanced money, against it, to the vendor .
Either way, off the wall or "off the chandelier" (for those who bid in posh places!) bids are common. That's why the old hands stand at the back of the room, leaving dozens of empty seats in front of them. That way, they can see whether there is a bidder. That won't stop the pretence that there are bids "on the book", commission bids submitted and recorded by the house beforehand, but it does help.
I've never heard of a prosecution of a "ring", though there have been for pretend auctions where everything is fraudulent, and the Act must be one of the least used on the statute book.