I worked in a bank when I was younger, and we would get American customers from cruise ship in a few times a month. They were just in town for the day, so would come in when the bank opened, get some Canadian cash then come back later in the day to bring back whatever they hadn't spent to change it back into American.
Oh dear, the conversations we had! I can't remember the exchange rate at the time, but the US dollar was worth more than CDN. So yippee, in the morning they would get $1.20 for every dollar of theirs, but somehow at the end of the day they wanted more, since their dollar was 'worth more'. Plus we couldn't exhange the coins. There were a lot of confused and unhappy customers.