Cool Stories, and I'm sure you have a great Dad, but he's no magician. He's just a reasonable guy that understands the value of privacy and discretion in negotiating.
Dentist- He asked you to go to the car because he was working out a payment plan. He was going to have to swallow his pride, and no father wants an offspring to see that. He may have got some docked off the price, but he was just working out terms. Honestly, do you think everyone who needs their wisdom teeth pulled has $2000 in cash on them?
Boat- That one is a little more interesting. My guess is that it was a combination of a beg and a bribe. Not the kind of begging you witnessed. But real, pride swallowing, humiliating begging, perhaps with a few extra bucks thrown in as a sweetner.
There is only a certain amount of self prostration a parent can do in front of their children before they begin to lose their respect.