Who was in the right and who was in the wrong in this situation?

I was at a mechanics this afternoon while a heated argument between a technician and a customer turned into a flaming war.

A man who is probably in his mid twenties was getting the alternator in his taurus fixed and when the mechanic told him how much it was the man nearly went insane. Everyone in the shop was quiet and terrified while these two argued and fought. The customer claimed he could not pay for the job but the mechanics told him he couldn't leave until he paid. The customer got furious and said things like, 'How the hell do you expect me to feed myself and my family for the next six months with this ridiculous bill!?' The mechanic initially said it wasn't his problem and that it had to be paid for. They fought for a few more minutes then they began yelling, more the customer then the mechanic. Then the customer agreed to paid grudgingly but as he paid he said, 'I hope you and your stupid company could use this money because God knows I needed it way more!" The customer said a few seconds later, 'Go buy yourself your stupid gaming console while my family and I barely scrape by every month eating oatmeal and canned food for every goddamn meal!" As the customer walks out the mechanic said something rude, 'don't blame others that you weren't smart enough to get an education.' The customer went ballistic then and started cussing and threatening to beat the trash out of the mechanic. They threatened to call the police on him. The man just replied, F you, then left.