The entire nature of "fixing" is black-or-gray market, illicit, exclusive, or otherwise non-retail connections. "Fixing" is not simply doing the shopping for someone who doesn't have the time, the balls, or the talent to do it for themselves That's "trading", "dealing", or just "gofering". Browsing markets and potentially using stats and skills in order to try to buy at marginally better prices than some other charmless baka sucker, and then sell-high to same, is not "fixing" either. Finally, a "topside fixer" is just a fixer, there's no such thing. But maybe they have a faceman for reeling in, or pushing to, the topsiders.
With all that in mind, the idea of hiding normal stores in a challenging layout does seem valid. Not for any buying advantage, but just to add something to the experience.