Many people just click on price update, whether the existing price is right or not, just for the points. After all, Waze is just a game for most people...it's all about the points.
It is so easy to manipulate prices, by entering pretty much anything you want. Waze backend is not intelligent enough to know what is a realistic price, and what is not.
And trust me, even the Waze programmers are not intelligent enough to write an algorithm that makes sense of elastic pricing theory, such that exists in the retail gasoline marketplace.
You are right though, in that the pricing database in Waze is worthless. Hey...guess what...the users get what they pay for!