Love this little fact I read on TodayIFoundOut.com:
The Baker’s Dozen has its origins in the fact that many societies throughout history have had extremely strict laws concerning baker’s wares. For example, in Ancient Egypt, should a baker be found to cheat someone, they would have their ear nailed to the door of their bakery. In Babylon, if a baker was found to have sold a “light loaf” to someone, the baker would have his hand chopped off. Similarly harsh measures could be historically found throughout Europe. As it wasn’t that hard to accidentally cheat a customer, given the exacting attributes required of the end product, bakers began giving more than what the statue outlined to make sure they went over and never under. Specifically, in terms of the “baker’s dozen”, in England…it became common practice that if a vendor or other customer were to order a dozen or several dozen loaves of bread from a baker, the baker would give them 13 for every dozen they ordered. Likewise, when selling any quantity, they’d give 13 measures when only 12 were purchased. This effectively made sure that the baker would never accidentally break the law and be subject to severe punishments.