Don't tend to do big wagers very much any more, and the one I have in mind was quite a few years ago, and a bit of a mistake TBH. I got the decimal in the wrong place and instead of a 0.50p each way bet for a total of £1.00, it got placed as a £5.00 each way for a total of £10.00. Got lucky with that one as it won at odds of 11-1 making me a lovely little £66.00 profit ...phew!!!