How do you make sure your employees aren't skimming money off of sales and foster a culture with a high level of trust?

For transactions where physical cash is exchanged how do you make sure you can trust your employees especially when you arent on site.Using a fleet of food trucks as an example how would you tactfully monitor the cash situation and minimize skimming off the top by employees?Im thinking of using high minded tactics such as a generous compensation and treating others respectfully but this wont work for the minority of those who have no qualms being kleptomaniacs.Without being too overbearing and soulless like a corporation or rough and mafia-ish like smaller outfits whats the standard operating procedure here? see hubwealthy.com/wealthy