Never ran into this, honestly. My local WalMarts are much more in love with 'This was the price on the shelf, this is the much higher price we're going to scan at the register, and surely you don't want to hold up the line for twenty minutes over a few dollars, do you?' Wrong.
But it doesn't surprise me. The golden rule of just about any business is 'Do whatever you can get away with,' and WalMart certainly qualifies as a business...