Why are sales people such crap heads?

The answer to that is simple. Most sales people are commission driven and if they don't feel they will make enough money from you, they treat you badly. Also, sales people are usally desparate to make a sale, so they will lie, cheat and steal to make a buck.

This is just a small % of sales people, most sales people are ethical, upstanding people. Not all sales people are rogues.