I think it takes a lot of effort and a lot of diversity in the art, often in addition to a related business like an in-house framing shop, to make a gallery profitable. It also takes people skills and an in-depth knowledge of the various art forms being sold. The most successful gallery owners I've known have M.F.A degrees, and while their galleries sell photography it's not their main source of income. They sell everything from ceramic, bronze, glass, metal, and wood sculpture, to oils and watercolors, and things like hand made jewelry and framing. Framing is always a big part of the income. I also know a couple of former gallery owners who went out of business. All sold only "wall art"; no sculpture, jewelry, framing, etc., and I think there's a strong connection. I also think that to some extent all of this depends on exactly where you are and what you are selling. A gallery on main street in a tourist location selling items related to that location will do a lot better than the same gallery selling the same things anywhere else. In most places people are decorating their homes and galleries have to sell a broad range of art. We also have a very successful art co-op nearby, and while they don't sell framing they do have a huge range of different art forms that changes every month or two. Just my 2 cents...