Clearing out a closet, attic or garage can be a chore. Old photographs, clothes and books can create clutter, or take up space that's sometimes needed for something else. But every so often, the heirlooms or mementos that you find retain some value: if that's emotional value, it can be hard to part with them. If it's financial, that can make it easier, as Willem Marx hoped it would be with his childhood stamp collection in London.