I've been fairly lucky over the years (touch wood!) and for most hiccups I've had the wherewithal to get it fixed, restored or whatever before anyone noticed...

I've been fairly lucky over the years (touch wood!) and for most hiccups I've had the wherewithal to get it fixed, restored or whatever before anyone noticed... ...Except the time I worked for a web dev company that had just set up a sideline selling product [1]. At that time we received maybe 5 orders per day and while I was integrating the payment gateway automation, we had to manually enter card info into a web interface. We had a lot of attempted orders from Nigeria so very strict verification was enabled and if you mistyped a cardholder name or address even slightly then it would fail. So one day we get an order for around £150. I enter this guys card info into the page and hit send. Bam! "Not accepted: please try again". I re-check his info and it's fine except my capitalisation is slightly different. I adjust and try again. Same message. I try a couple more variations with no luck. I phone the customer and find his card actually has 'Mr' on it. I try that and nothing. I try 'Mr.'. And so on and so on. Eventually I give up and tell him to send a cheque but we'll dispatch today. Couple of hours later we get a call from an irate Mr Johnny Customer. His bank have just informed him that we've charged 16 x £150 to his card. Turns out that the address verification would only fail after a charge attempt was made - and then a request made immediately to void. However, for debit cards, the voided process can take 3 days and his card was useless in the meantime. Not too bad in the scheme of things, but this error was over 3 times my monthly wage at the time and I'd only been there 2 weeks. [1] specifics removed as they've since gone on to become quite a big deal (from the solid foundations I built I presume!) and Google can be a harsh mistress.