A few months ago I picked up 6 or 8 plasitc storage boxes at WalMart.  They were not individually priced, nor was there a price on the shelf - I needed them and they were usually $9-10.

The clerk grabbed the first one and rang it up for the count.  I slid my credit card and noticed the charge was real low.  They rang up at ~$2 each.  I brought it to the clerk's attention that it was probably too cheap.  She called over a manager.  The manager had her scan the other boxes and they each rung up ~$10 each.  The box she first rang up had a different tag with the correct item description - different skew number.  The manager said it was their mistake; I got them for ~$2 each - sure wish I'd picked up a couple of dozen.