I use Lightroom, I created a collection of images I've sold, and just move them into that collections, and set keywords for customer and location etc. I have collections for Instagram, Twitter, FB, my other site and gifts. The way LR works, is a collection is just a pointer to the original. I allow have folders that has a hierarchy Starting with Customers folder at the top, and customer/gallery name below this is also accessible through Lightroom. Some of the files names represent the sale, i.e bobjones550061716metal which means sold to Bob Jones for $550 on 06/17/16 Metal format. I also use a spreadsheet that calculated profit, using creations costs, shipping, gallery or show percentage, markup and resulting profit. Allows me to do "what ifs" These are mostly for things I do off FAA. I haven't sold much here, but I figure their database has enough info that I can use it as it is. Only thing missing is customer info. :(
Of course all my work is digital, which my way isn't much help to painters and sculptors that deal with physical presence ;)