I was at a customer site in central London installing some thin client PC's and the head bod there asked me to make sure that her local printer was connected. Looking at it, it was connected to her old PC by a parallel cable, but the thin client did not have a parallel port. The printer did, however, have a USB interface, but it required a cable with a USB-B connector, which I did not have with me. I was 100 yards away from Tottenham Court Road, so I knew I should be able to pop out and get one, so that's what I did. The first shop I found one in wanted £15 for a 1m cable - I had bought 2 x 1m of the same type of cable in my local Tesco the week before for £2, so I queried the price. After a bit of haggling, he eventually sold it to me for £10. Luckily the customer was paying.