Thanks! This is very useful information.

1. I obtained 6 quotations from 6 different contractors;
2. I ensured the contractor write down the critical specification: 8" gravel, 2" binder course, 1.5" top course after roller compression.
3. I printed out the standard procedure of paving asphalt driveway.
4. I showed the diagram of specification to the worker and he was first not happy but follow my suggestion because mine was right.
However, whenever I left the scene, they cut the corners: not evenly dug down; quickly put on a thin layer of gravel so nobody know how deep the gravel layer is; laid down asphalt mix less than the specified thickness .....