"Unauthorized 135 operations continue to be a problem nationwide, putting the flying public in danger, diluting safety in the national airspace system, and undercutting the business of legitimate operators... (two main pillars of misunderstanding remain) "the misuse and/or misunderstanding of expense sharing between pilots and passengers, and the apparent lack of understanding of pilot privileges and limitations versus operating rules."
Source: In a follow on to a May 2020 informational pilot letter, amid a continuing operation to address unlawful and illegal air charter operations, the FAA has published an infographic for use at airports throughout the airport system.