London's Bicentennial (Snippet 52)

 Drinking in London - 1837
   “Besides the seven taverns there is a number of little grocery stores which are, in fact, drinking houses. And though a law exists, which forbids the sale of spiritous liquors in small quantities by any but licensed publicans, they easily contrive to elude the law; as thus:- a customer enters the shop, and asks for two or three penny-worth of nuts, or cakes, and he receives a few nuts, and a large glass of whiskey. The whiskey, you observe, is given, not sold, and no one can swear to the contrary.”

Source:
  I found this in an older post I did about General Stores in Canada. The quotation is found in Carol Priamo's book, The General Store, pp.21-22. I have not re-checked, but you can find a copy of the book in the LPL. 
Bonus: There are fewer variety stores now and the owners are likely fairly desperate. One could try this idea again. For example, one could sell a bag of Doritos at an inflated price and then 'treat' the customer to a Margarita.