Both parties are more than happy to stick it the "customer" and see if they can each get a little bit more money or pay a little less. Neither party is remotely interested in finding a quick and easy solution for the "customer" but will both insist that the other party is completely at fault for the billing error/refusal to pay.

The entire system is full of fraud from both parties and you will get taken to the cleaners if you don't watch each and every bill that comes through.