There have been a few close calls when I've nearly ordered something in that ridiculous 1/72 scale thinking 'that's a good price for 1/48'. The sooner 1/72 is stamped out the better.
The biggest bo-bo I've made ordering online was when I was buying a second hand digital camera many years ago. I entered my bid in the last few seconds of the auction and didn't double check the amount, only to realise when I hit enter that I'd missed the decimal place, bidding about £4000 for a £40 (ish) camera.
Apparently screaming at the computer doesn't make any difference to the bidding process. Oddly enough I 'won' the camera and my heart started beating again when it automatically bid just enough to secure the purchase – more than I really wanted to pay, but a lot less than it could have been.
I'm more careful now.