Sure. Think of Ethereum as a global computer that coordinates human interactions. On top of it, you encode the rules that those interactions should follow, and

Sure. Think of Ethereum as a global computer that coordinates human interactions. On top of it, you encode the rules that those interactions should follow, and a mechanism for recording who has been following the rules and who hasn't. A decentralized Uber would have logic that records how often drivers show up when they offer a ride, how often they're late, how clean their cars are, etc. It would have similar logic for riders to handle their end of the interaction like the one you pointed out: did they pay what was agreed on? The payment mechanism is irrelevant. Driver and rider satisfaction is what matters, and that's easy to track without putting any limits on their real world interactions.