At the end of the trip, I just thank the rider for being a great rider and for that I am giving him/her 5 stars. Also mention to them they can rate the driver from the Uber app right away. I make sure they see the screen with stars before they leave. Of course I don't submit until they leave so the ratings can be changed if needed. 80% of pax say they will do likewise and sure enough they do. After I started doing this, my non-raters dropped from 35% to 27%. And of course ratings climbed 0.05 as well. Not saying this strategy will work for everyone but worth giving it a try.