"No one else has complained of this problem"

I was sending donations to an organization. The treasurer was lazy about making deposits and would sometimes hold onto my checks for weeks. Considering that banks now offer photographs of checks from a cell phone, you'd think that that would be a thing of the past.
So they nagged me to send a donation by credit card. Oh, and they suggested that I add a little more to cover the cost of using the credit card. I'm not a big fan of using my credit card with small fry companies, but I shrugged and said to myself, "What could happen?"
Well, I got charged twice.
When I told the person who encouraged me to move from check to card, he said that I had probably hit the button to request the transaction be continuous (yeah!, right!, on the same day?). Then he wrote that no one else has ever complained of having this problem.
That was the proverbial straw that broke the proverbial camel's proverbial back. No more money from this user.