They actually have been sued and with some degree of success. I know of two civil lawsuits filed against Mastro Auctions since they ceased operating (though there may be others). Both lawsuits were also filed against Bill Mastro and Doug Allen personally. Both lawsuits were settled to the satisfaction of the parties claiming to have been damaged by Mastro Auctions.
One lawsuit was filed in February 2014 by Dr. Howard Rosing (a very longtime advanced collector and true gentleman).
Below is a link to an article about the Howard Rosing vs Mastro et al lawsuit. The lawsuit was settled very quickly. Because a confidentiality agreement was signed, Dr. Rosing was not at liberty to tell me the details of the settlement, only that it occurred, and that he was very pleased.
The complaint involved four single-signed baseballs that Rosing purchased from Mastro Auctions between 1998 and 2001 for a total of $134,000. According to the complaint, "Rosing has since learned that the four baseballs are in fact counterfeit" and his $130,000+ in damages were "caused by Defendants' fraud and/or negligence." The four single-signed balls were: Mickey Welch ($20,217), Jack Chesbro ($20,898), Frank Chance ($21,836),and Henry Chadwick ($61,251). Extremely interesting note that is not mentioned in the following article or the text of the Rosing complaint: the Henry Chadwick single-signed ball was consigned by Peter Nash. And the Mickey Welch single-signed ball also originated from (that is, was previously sold at auction two years earlier by)....Peter Nash.
Article Link:
https://www.sportscollectorsdaily.co...ned-baseballs/
In June 2009 when Mastro Auctions sued Dave Forman for $400,000, Dave Foreman countersued for damages relating to various issues including shill bidding. The countersuit prepared by Dave Forman's brilliant attorney in the case (Jeffrey Lichtman) was extremely detailed and devastating. Instead of collecting $400,000 FROM Forman (who did not dispute having an unpaid auction balance, but did dispute the exact amount), Mastro Auctions not only dropped and completely abandoned their entire claim against Forman (lowering the $400,000 to $0) but also returned over $100,000 in cards to Forman that he believed were owed to him, and, in addition, Forman actually received a payment of $3600 in the settlement. (Hard not to say "wow" to that complete turnaround).
Links:
https://www.sportscollectorsdaily.com/a-fine-mess/
http://www.nydailynews.com/sports/ba...ticle-1.428887
http://www.nydailynews.com/sports/mo...e_desktop=true
https://www.google.com/amp/www.nydai...ticle-1.121333