I'm sure that cameras are exactly like many other collectables, antiques, coins, stamps, etc. A rare stamp has a "catalogue value" quoted in one of the recognised catalogues (e.g. Stanley Gibbons, or Scott), but this is very much a guide, a true buying or selling price depending entirely on condition, availability, collector demand on a particular day, whether the sun is shining and people feeling generous, etc., etc. A "catalogue" value also reflects a dealers price, including all overheads and the cost of holding a large stock and variety of items. An offer on Ebay may well be a collector to collector deal, without a dealers costs or profits to be covered.