stealth shopper
n. A person who shops secretly to avoid flaunting wealth or to hide expenses from a spouse; a person who purchases expensive items that do not look expensive.
Other Forms
Sheepish about stepping out as the credit crunch bites, lovers of shopping are hiding behind their computers where they can spend, spend, spend in complete privacy. The web offers the perfect opportunity for a new breed of 'stealth shoppers', embarrassed about flaunting their wealth, or what is left of it.
—Alice Fisher & David Smith, “Stealth shoppers shun stores and splash out on luxuries online,” The Observer, November 30, 2014
But such obvious excess is seriously frowned upon now. The shopaholic is now a "recessionista," proudly wearing last year's "It" item and claiming that not only is it years old, but she got it at Winners.

The entire language of fashion is shifting, and the new frugality is dictating the vernacular.

The shopaholic, fashion victim or fashion-lover is now a "stealth shopper."
—Tracy Nesdoly, “Confessions of a stealth shopper,” The Toronto Star, February 05, 2009
1992 (earliest)
Michelle, a successful writer and editor, fears the day her husband might discover her secret stash of credit cards, her clandestine post office box and a host of other tricks she uses to hide how much money she spends on herself.
—Jeanne Wright, “Charge of the lie brigade; Secret credit cards and other surreptitious strategies are just a few weapons stealth shoppers wield at orange county malls when their mates aren't looking,” Los Angeles Times, October 25, 1992