One of the best systems I have come across for hanging work in a gallery was at the Edward Carter Gallery in NYC. They hung the framed prints on large, 4x8' wide panels. The panels were made of plywood which was then lightly padded with batting and then covered with a fabric with a slightly coarse weave. The effect was that no matter how many times you put a nail in the panel, it never showed a hole. They never had to paint, the walls always looked perfect and if they sold a large piece off the wall they could easily replace it with any size piece without worrying about moving the nail and leaving an exposed hole. It was also a very attractive way to show art and it also added a certain amount of sound deadening to the room. So many galleries are loud because of all the hard walls and no soft materials.