I also haven't had Waymo assign a car and then decide to assign it elsewhere sometime before arrival.
I have had Uber/Lyft cars that were going to come to me and then some time before picking me up, they change their mind and I get to start a new wait for a new car/driver... worse, I've had that happen a few times in a row on some occasions.
I've seen more in the 10% premium ballpark for most Waymo rides (for just the base fare, excluding tips). There was a very stormy day once where the price shot up pretty high very quickly, but that's not the norm I see.
As an aside, Waymo does have a feature which allows you to add stops that, if within certain parameters like the trip being within 30 minutes (I believe) that it kinda treats it as one trip which is rather cheaper than multiple independent trips.
So, for example, I had to pick up my kid from school the other day and found out last minute I wouldn't have a car. So I booked a Waymo, selected my destination, and then also selected that it would be "round trip" in the app. The car got me to the school and an option in the Waymo app for "ready for pickup" was available; the car left after it dropped me off. After my kid came out, I clicked that ready button and another car came to the school and took us home.
The price for the round trip was just over $20. The price for two independent trips would have been about $10 more (if I'm calculating & remembering correctly). So another interesting feature on the pricing discussion which, to my knowledge, isn't an option with the other ridesharing/taxi businesses.
I have had Uber/Lyft cars that were going to come to me and then some time before picking me up, they change their mind and I get to start a new wait for a new car/driver... worse, I've had that happen a few times in a row on some occasions.
I've seen more in the 10% premium ballpark for most Waymo rides (for just the base fare, excluding tips). There was a very stormy day once where the price shot up pretty high very quickly, but that's not the norm I see.