To determine the value of an item, one must take into account three factors, condition, rarity and desirability.
Condition:
Condition starts at perfect and works its way down. Collectibles
of the sort we are dealing with were not designed to last for years.
When a relic is found the degree of its preservation is
determined by either foresight or luck. The laws of physics
remind us that all things will decompose eventually: Therefore
preserving your collection requires effort. All valuables
should be kept out of basements, garages and attics where
temperatures can vary wildly and humidity can be high.
I have stopped being surprised when collectors, opening their boxes of cans for the first time in years, tell me “Boy, I remember these cans being in much better condition!” Even collectibles protected in climate-controlled rooms are not immune to tarnishing, fading or drying out. Preserving these treasures requires maintenance. While you own them you have a duty to keep them well.