That’s cheating their company (and/or setting up for tax evasion), which in my experience is far more common than cheating the customer with a detour, at least when the customer is local (you can show your localness through verbal cues implying or simply indicating you know the route).
Only the other night a Chicago cabbie tried to get my wife to pay with a portable credit card reader not the one installed in the machine. She made a big fuss and he 'discovered' that the built in machine was working after all.
