I was in the biz too for a while. There are testers onsite of every city job testing the mix, the compaction, the crown and a myriad of other specs. As well, the company owns the road for two years after, and is responsible for any repairs or failures. After 2 years, it is turned over to the city.
The company I worked for does the complete job from raw land to paved road. Some areas, the soil conditions are crap and things are challenging, but they are able to lay down a good road that withstands the wild temp extremes from 90 above to 40 below. Roads here last 40 years before they are top-lifted.