Eurekalert is carrying a blurb about social cues affecting people's spending decisions. Consumers will choose a more expensive brand-name item if an unknown fellow-shopper is standing near them in the aisle. The cool thing about the effect is that the stranger is not directly involved in the transaction-- it is the "mere" social presence which has a measurable effect on the purchase choice. In fact, the researchers also chose an invisible product-batteries-- so that the social impact of the brand name should have been minimal after they were in use.
The effect of an onlooker gets stronger if there are more people, or if the onlooker gets physically closer. But the experimental subjects actually did not report any feelings of annoyance or defensiveness until there were three people up close. (The famous Wall-mart Oxygen Deprivation Effect.)
The items to be bought in this study were just batteries, but I can imagine the impact on deodorant sales. In fact, this consumer effect, which has been branded as "Social Impact Theory," probably contributes to the embarrassment effect on buying more socially visible things.