[zobzu]

actually every time you dont leave a good feedback, uber will contact you back to clear it up and contact the driver (will not say who left the feedback) and ensure this was legitimate or otherwise reimburse your trip (on top of making sure the driver's star score is severely affected)

if you're a customer with 4-5 stars rating you'll get 4-5 stars drivers, always, all the time.

This makes the probability of bad services very low (and in fact null in my experience so far - i'm pretty sure they select 5 stars by default for your 5 first ever rides too)