There's in app-tipping in lyft. The driver doesn't know whether you've tipped them or not when they rate their experience with you. Moreover, it's relatively difficult for the driver to disentangle who tipped them what from their daily report at the end of the day[0]. So you really can pay based on what your judgement of their service level is.

[0] I did once got into a very friendly chat with the "owner of the world's second tallest yacht" (checked it on wikipedia; totally legit) and was memorable enough that I was curious if he tipped. He didn't.