Bragdon powders are useful but very aggressive, its very easy to overdo them and difficult to fix if you do. I only use them for rusty, grime crusted junk. And keep the bags safely away from your model, if you grab an open one, or drop one, they're liable to create an HO scale environmental disaster when they blow pigment everywhere. I know because it happened to me. I don't like alcohol and india ink for anything other than heavily weathering bare wood.
For subtle weathering effects, such as you'd want for a well maintained grocery store, I would use artists oils in a thin wash. The 1/35 scale armor modelers have oil washes down to an art form. The results look natural and very convincing. Consult the relevant forums like Armorama.com for how-to details.
One nice thing about this method is you can apply it in thin, barely perceptible layers or "filters" as they call them, so you minimize the risk overdoing it. Anyway, practice on scrap first. Its cool to save your scrap test pieces in a file, with notes on what you applied. Something that didn't work for the current project might work for another.
Dave








