Lost Opportunity

Visiting with my folks over Christmas, they told me about their neighbors who recently came into a bunch of coins and currency. Her father had owned a vending machine company for years and had collected what he found. I don't know the details, but the lady said that it was "tons and tons of coins and stuff". My mother told her that when I came home I could bring my books and help them sort through the stuff they had and see some approximate values. I'm no expert, but I could at least give them some ideas of rarities.
I would have loved to go through it just to see what they had.

Then next time my mom talked to her, she said that they didn't want to do that, they had just taken their stuff and sold it to a dealer. In addition to a bunch of coins they had about $500 face of $10's, $20's, and $50's that had "the name of the bank printed on it like National Bank of Kansas City" they also had a $100 bill like that. I'm assuming they were national bank notes.

The dealer gave them $120 for the $100 bill and face for the rest of the bills. My dad was so mad he told them "Oh, that's too bad, my son would have given you more, he's been buying those for 5x face" (he had no clue he was just irritated that they were so dumb they would sell something without finding out what it is worth first).

I can only assume that they got hosed on the rest of their stuff also. I told my dad that if something like that ever comes up again that he should go with the person to the dealer (to verify the quote) and then give them 10% more than what the dealer offered. He and I could then split anything we made or didn't.