I would draw everyone's attention to the Uniform Commercial Code of the United States, which states in section 2-328 (4):

If the auctioneer knowingly receives a bid on the seller's behalf or the seller makes or procures such a bid, and notice has not been given that liberty for such bidding is reserved, the buyer may at his option avoid the sale or take the goods at the price of the last good faithbid prior to the completion of the sale. [Emphasis added]

You did not provide advance notice, therefore you acted unlawfully.