telephone
electricity
water
gas
We all get an account for these 90 days after we have started consuming
All of these are credit accounts and have lots of terms and conditions.
Water is sometimes charged up front in rural areas when picked up in tanks. Gas / Propane is often charged "at time of delivery" in rural areas. My cell phone provider "precharges" for a month's service. Getting sufficient electricity delivered in handy storage containers is a bit tricky hence the monthly charges and "pay as you go" metering.
The question to me is what did that guy think he was buying??? He asked for labor, you (OP) quoted price on labor, then he wants to base payment on quality of materials, not quality of labor???
I once worked for a guy that "took back" some auto body repair work when the customer refused to pay part of a bill. This work was in addition to some insurance work. Most of the charge
(about $400) was worked into the insurance bill but about $50 was left to cash and the customer felt he shouldn't pay anything. To my understanding everything had been discussed and OK'd up front so this was like renegotiating after the work was done. Car owner kept returning with "work quality" complaints as a justification for lack of payment. Eventually shop owner got pissed, said "You're right, I can't do it the way you want" and walked out to car with a small grinder. Took about 30 seconds to remove the paint and filler that had been used to hide several hail dents in the hood. While the car owner was tripping over his jaw the boss said "We're square now" and walked back inside.
Please keep us updated if you find out how the kid's dad responded. I might be tempted to bring over whole length logs and threaten to drop 'em then load up the splits to take back home if payment isn't forthcoming. "And I won't even charge ya for the cost of fuel or the labor to load 'em in my truck." Can't imagine Mr. Professor getting much sympathy trying to lodge a formal complaint about that one.