Where Facebook functions, IMO, is when you have already clearly established your brand and have identified a precise target market by which you are seeking a way to remind them you're still alive. Facebook does not work for artists who are looking for sales in the short term (under 36 months) especially when it's on an overly generalized market (some branding specialists feel that with regards to the creative arts this period of minimum duration should be 5-7 years). Selling a print doesn't make a photographer a business, although that is the common metric we tend to want to use.
Short Answer: Facebook can work, but it's just one small element involved.