One difference is the asymmetric information. There are hundreds of places to determine the fair value of your car. However your HR department uses every dracon

One difference is the asymmetric information. There are hundreds of places to determine the fair value of your car. However your HR department uses every draconian policy available to keep you from knowing what your coworkers make. Until Glassdoor came along, it was very difficult to know what you're worth, and its dataset is still quite sparse. Go around and ask most people (i.e. non-tech) what they make relative to their coworkers and industry and they probably don't know. Hard to auction yourself when the numbers are secret.