The FAA is serious enough about it, they've opened an illegal charter hotline. From the AIN Online email newsletter...
[FONT=Verdana, Arial, Helvetica, sans-serif]FAA Grant Funds Illegal Charter Hotline
The FAA has provided grant money to fund a hotline for charter operators to report “suspected illegal commercial activity,” according to the National Air Transportation Association, which is administering the system. The hotline–(888) 759-3581–is designed for employees or agents of Part 135 charter certificate holders to report activities that they suspect are illegal charters, NATA explained, “where an aircraft operator without an FAA Part 135 certificate is accepting compensation for transportation, in violation of both FAA and Department of Transportation regulations.” Illegal charter is a perpetual problem in the charter industry, affecting safety because non-certified operators don’t meet Part 135 standards and also undercutting revenues earned by legitimate charter operators. According to NATA’s “Risks of Illegal Charters” guide, “Illegal air charter operations are prevalent around much of the U.S. One review of South Florida’s Yellow Pages and FAA records indicated that 14 of the companies listed were operating a charter business illegally.” Hotline callers can report anonymously and will receive a case number. Details of the case will be provided to the FAA, and NATA will follow up to ensure the agency is taking appropriate action. The hotline is staffed by an independent third-party, according to NATA.[/FONT]