Lisa has a fantasy of being wealthy enough to buy an American Gold Eagle coin (face value $50; actual value around $600 depending on the price of gold) and try spending it to see if the merchant will take it. Of course, if anyone had ever tried to pass me a $20 gold piece when I worked in retail, my reaction would have been to have accepted it before the customer changed his mind, then change it back out of the till into my own pocket. What Lisa wants to know by such an experiment is how intelligent the person behind the counter is.

(The real trick would be to get a much older pre-1930s gold eagle or double eagle, but those were demonetized in 1934, and I don't know if they were ever technically reinstated. You'd still be a fool to not accept it at face value, but you'd at least be a law-abiding fool.)