When stock goes off-condition
Updated
A dealer's stock is a collection that happens to be for sale, and it fails the same way.
Stock decays like a collection
Material held for sale sits in flats, often in dealer cardboard, frequently in a garage or a storage unit, and usually without the environmental control a display collection gets.
Which means stock is systematically stored worse than the collection, and it is the material with the least documentation.
What to check
Sulfides for the first bloom of decay, which is the one that spreads.
Carbonates for efflorescence, which tells you the storage is producing acid.
Labels for embrittlement and for separation from their specimens.
Boxes for the beginning of breakdown: a foam going crumbly, a plastic going cloudy or sticky.
And the humidity in the space, which for most dealers is whatever the building does.
Rotation
Sell oldest first, which needs an acquisition date in the catalog rather than a memory.
Review anything unsold after a year: it is either priced wrong, presented wrong, or in the wrong channel, and holding it costs storage and condition.
Material bought in bulk lots is the usual backlog, and it is the material most likely to be undocumented.
What to do with it
Rehouse anything staying more than a season. Dealer cardboard and newspaper are transit packing.
Discount honestly rather than shipping declining material to a customer, who will notice.
And use the stock that will never be individually catalogd as teaching sets or bulk lots, which is a real market and clears space for material that earns its shelf.