Re: Yada yada
"Boots Opticians used to alternate 50% off and 2 for the price of 1. No idea how they got away with it for so long."
Because if you went during the 50% sale, and bought 3 glasses, you'd effectively pay for 1.5 glasses.
And if you went for the 2 for 1, and you bought 4 glasses, you'd pay for 2.