My mum was going to throw out a wrist watch and I have kept it as I think that it may have some value. It is a commemorative watch of Princess Diana and Charles, from around the time that they got married. It is still in good working condition. I just have no idea if it is one of those worthless souvenirs from the time or it may now be a rare item worth something, even if not much. Where could I go to find out if it is worth selling?