One of the small but nagging issues which will need to be resolved is how to deal with "items left behind".

When more people begin to use public cars for personal use/hire people will begin leaving phones, strollers, jackets, wallets in these vehicles. Unless the cars are to have omnidirectional cameras or electronic trackers to monitor everything, people are going to lose things. This is going to be a pain point. It might be just becoming aware -as people do in taxicabs but at least honest cabbies will return items as its in their interest to maintain good reputation --a stranger is only bound by altruism.