Maybe I've been lucky, but I don't recall being (knowingly) ripped-off until this year.
Incident 1: a few weeks ago I sold something on eBay to a guy from Lockleaze in Bristol. He turned-up, seemed like a straightforward likeable bloke and paid cash. We chatted and agreed on something else for £10 which he suggested I invoice him for; I trusted him so let him take the item. The invoice has been ignored, as have text messages, emails and phone calls. I just don't understand why anyone would be petty enough to steal something to save a tenner. I'm tempted to name him here but live in hope that it's all been a mistake and that he's changed his mobile number (and email address!)
Incident 2: last weekend I was in a great London pub called the Fox and Anchor in Clerkenwell. I bought a couple of drinks and commented that the price seemed a bit high - the barman checked and said that the prices were correct; I couldn't see the printed price list so I shrugged my shoulders. Guess what ... the next drinks (served by the landlord) were cheaper. I mentioned this to the landlord who "had words" with the previous guy who then handed-over 20p with a "don't spend it all at once" comment!
I feel much better for this rant and will now return to my leafy idyll, here in Stepford :-)