Prices can go down

Someone e-mailed me a question over the weekend wondering why the price of a 1970-S proof set with the error no-mintmark dime in it declined over three years.
He happened to have found two in an estate’s safe deposit box.

Apparently rather than being happy with the unexpected find, he was concerned with the decline of the retail price of $1,350 in a 2008 edition of North American Coins and Prices to $1,050 in the 2011 book.

I had to respond with generalities because there is no factor that affects the error set price alone. Nobody found 200 more in a secret stash and the error hobby has not turned against the set.

Other proof set prices have also declined in that time.

The odd thing is that their decline has been in part due to the popularity of proof sets over time.

Collectors who buy the current U.S. Mint proof sets year after year are also most likely to be affected by the economic fluctuations hitting the economy as are the dealers who serve them on the secondary market.

If a collector needs money, what is the best way to raise it quickly at a shop or weekend show? Bullion coins aside, it is proof sets. They are readily tradeable.
Dealers who need fast cash also tend to dump proof sets.

Why? A major reason is that when the economic difficulty passes, they are fairly easy to replace.

Most collectors and dealers are in it for the long haul. They know if they sell something that is truly scarce or hard to find that when they go to sell it they might find that the specialist is on vacation that week, or a shop owner wonders if he can get his money out at any kind of reasonable level because his client base has gotten tighter with their hobby expenditures.

They also know that the scarcer the item, the harder it will be to replace at a similar price in the future when the economy and their place in it improves.

Is this a good answer?

It is the only one I have.