Thinking back over the years to the (rare) times this has happened publicly on here before, I'm not sure I can remember a single time when it turned out to be a case of fraud. A few times it was a genuine misunderstanding, but almost invariably it ended up being a simple case of human fallibility. In other words, some disorganised bloke, leading a chaotic life, just getting himself in a bit of a muddle.
Up to you how you handle it (I do love a good hanging), but do be conscious that (thankfully) you're probably dealing with a fool rather than a knave.