Miami-based Platinum Luxury Auctions LLC was supposed to be in the business of selling luxury real estate. But a competitor claimed it instead spent its time executing an elaborate and clandestine scheme that included mailing damning dossiers to the media and the rival’s wealthy clients.

The plot had immediate and expensive repercussions, according to alleged target Concierge Auctions LLC. It derailed Concierge’s auction of a $7.5 million property under contract for client Richard Peacock—a deal that cost the company more than $400,000 in commissions, according to court pleadings.