I usually start the conversation with "You must bank with Wells Fargo, Bank of America, or USBank.."
To which they replay "yes I do"
Then I tell them that those mega banks will take "temporary authorizations" and hold them for a few days trying to generate overdraft fees on their accounts. Usually the small banks, and the small credit unions don't play those games. I tell them that their bank knew that night that I only charged them $3 on their $15 temporary authorization, but it is their system that is playing games with them.
That usually ends the conversation.