Back in the 80s Esso started giving people Tiger Tokens every time they bought petrol. These tokens could be redeemed against a number of exciting items, and one of the most popular was a very desirable set of china mugs. Far from being viewed as a tacky free gift I remember seeing many sets of these mugs proudly displayed in the houses of my parents' friends. These mugs were a literal embodiment of your smart shopping, advertising that you managed your money wisely through the medium of pottery. This was one of the first successful loyalty schemes, but how *did* Esso's china mugs make your friends nicer?