How do you know if the guy you hired to drive your taxi is working or whether he just claims that there are no rides available?
If you don't trust your employee, you can fire them. Don't hire people you don't trust. If a company doesn't even know what kind of traffic, output, or variation in work an employee will have in their job then they are a bad business. Business takes on liability of the people they hire, and they should not be shielded from their own ineptitude in hiring and training them.
If there are no rides then what am I paying for?
If he brings in revenue, keep him. If he doesn't, don't. How is free market capitalism such a hard concept for Americans to understand these days?