Paul A Young's Foursquare offer

I discovered this one yesterday as I was walking through Camden Passage, near Angel in London.

When you check into the chocolate shop Paul A Young on Foursquare you get a free truffle (price £2.00).  No conditions, no quibbles, just very straightforward.  Of course once you're in there you feel honour bound to buy something else (I did anyway), and so it works well in getting you into the shop.  The offer is also valid at the other branch, in the Royal Exchange.

If people start to exploit it they can turn it off.  In the meantime go there and claim your free chocolate!