I don't mean to be negative about the idea, but I think there's an equal risk of it seeming less legit; Depends what size of businesses or what kind of services you're trying to offer but at a certain level I think it could definitely imagine a customer looking past an MSP in a retail location because the look like a "computer shop" rather than a legitimate business-to-business provider.

I don't think you're wrong about the value of visibility, but I think it would be a lot more advantageous if you could find a highly visible non-retail location, like an office location highly visible from a high traffic area like a retail development where you'd have the ability to put some form of advertising up or at least a front door with a big sign over it.

But I realize the reason for your question is probably the rarity/expense of such a location, and the affordability/glut of retail spots in some places. I think it would really depend on the place and it hinge on avoiding the "computer shop" look and I think that'd be pretty much impossible if it's like between a liquor store and a dry cleaners or even in the same strip mall as that kind of retail.