In recent years, a number of high street shops (such as M&S, Gap and Topshop) have employed "Vanity sizing" as a way to boost sales. This is when the sizing measurements are increased without changing the size on the label so the customer thinks they are fitting into a smaller size than they really are.
The symbolic consumption perspective proposes that consumers consume more than just the physical product that they have bought, but also the symbolic meaning of the product they are buying. It states that this makes purchasing the goods a significant element in the construction and maintenance of the consumers self identity, in the attainment for social status and in attempts to make oneself 'feel better.' (Elliot, 1994; Friese & Koenig, 1993).
I know, from being a girl and hence interacting with girls, that a woman's size, weight and appearance in general is very much a factor in their self-identity and their perceived social status.
According to this theory, a woman buying a dress would help construct her self-identity- this would be a more positive construction if that dress is nearer to the size that they would like to be and hence, they may be more likely to purchase it. It is possible that buying said dress would also make them 'feel better' about them self since they would think they had lost weight/were smaller than the last time they bought a dress and hence they may be more inclined to buy this item that made them feel good.
I think this is a very intelligent (if a little deceptive and cruel) tactic to employ as so much emphasis is placed on a woman's weight, dress size and general appearance. I know that in the past, I have bought a garment purely because I was proud that I could fit into a size so much smaller than my regular size. I am probably a living example of Vanity Sizing successfully persuading someone to buy!
Elliott, R. (1994). "Addictive consumption: Function and fragmentation in postmodernity."
Journal of Consumer Policy, 17, 159-179.
Friese, S., & Koenig, H. (1993). Shopping for trouble. Advancing the Consumer Interest, 5,