Although Uber would probably prefer that someone rides with them again and tells their friends/family about their pleasant experience, rather than squeeze a rider for a few more pennies. Their helpful community managers and system for doing a fare review certainly give the impression that they are looking at building a long term business. As a pre-IPO startup facing regulatory issues in a number of cities, they really don't have the luxury of offering a bad customer experience. The alternative is also simple, if someone has a bad experience, they don't have to use the service anymore.