Last year I made about $ 2000 USD off of others stupidity.
Here are my biggest money makers:
1) I purchased a boat load of supplements and asked for 3 days shipping, on the 4th day I called up and asked why I had not got the shipment. They told me they would ship the next day, I said forget and got a refund - a week later they showed up on my doorstep $ 500 USD
2) I put a down payment on some orthepedic inserts, went to pick them up and they never asked for the outstanding balance... 400 USD
3) I purchased 5 cases of tuna, the checkout girl charged me the price of 5 CANS of tuna..... 100 USD