Retail store Claire’s Accessories is currently running a ‘3 for 2’ promotion at a number of its stores. The normal convention for such offers is that you pay for the most expensive two items and the cheapest is free. Most retailers will explain this, in a very simple form of words such as “Cheapest item free”. You can’t make it any easier to understand than that.
But some clever bod in Claire's marketing department has decided to reinvent the wheel. The sign in the window says “Buy 3 items and the third lowest item is free”. Third lowest? The third lowest out of three is the most expensive. Poor punctuation and bad grammar changes the intended meaning. Fortunately for Claire’s, their average customer is unlikely to notice, given that grammar is rarely taught in schools any more, like what it used to be.