Brownie points in modern usage are an imaginary social currency, which can be acquired by doing good deeds or earning favor in the eyes of another, often one's spouse.
A popular etymology is an allusion to the merit badges or six points earned by Brownies (junior Girl Guides/Girl Scouts) for carrying out good deeds.
The relationship between a purchase and the collection of these "brown points" equated with doing a good thing (supporting the local vendor) and getting a bonus (the valuable stamps).
The boys received a small commission; in addition, if they met certain sales targets, they could also earn company scrip, consisting of green and brown vouchers, referred to as "greenies" and "brownies."
Its frequent appearance in newspapers in the 1950s date back to the earliest known usage in 1951, where a man in the Los Angeles Times speaks of earning favor with his wife in terms of brownie points.