I believe that grandparents point was that by not taking on any debt they don't have a credit score which can be verified. You can't verify something that doesn't exist in the first place.
However since all of the OP's examples involved credit (car rental post-pay, phone usage post-pay, etc.) then in those cases trust===credit score. Without a credit score, you're basically asking someone to trust blindly that you'll pay back a debt since there's no track record of your ever paying back debts.