The process of consumer stereotyping
may be defined as the formation of generalizations
about consumption objects
possessed or used by members of a particular social category
For example if you are using luxury brands you might be named as a label whore by other people; and later people will start making further assumptions about your income (saying you are one of the more affluent), whether you are old money or not, your job, where you live, where you shop, what you eat, etc.
The main reason for such associations is the fact that human beings usually economize their mental processes by using schemas and categorizations so that they do not have to think extensively before making a decision. The former is somewhat a blueprint of a social reality (eg: a person, an event), that is expected to exhibit an average example; while the latter is an artificial taxonomy of those blueprints in human brain. The schemas are established by past experiences and general social norms within a given society and then categorized cognitively.
So when one sees a Prada boot, first s/he identifies it as a luxury brand; if s/he cannot identify there is no association at all and the game is over. If there is any way that person relates to this brand, then it is taken as a cue to evoke the schema of whoever s/he thinks would wear such a brand (eg: label whore, celebrity, blue blood, a person who is trying to look richer than s/he is, etc) , bringing all the associations with it.