Initially, I want to caution readers who are now or will in the future have a part in disposition of an estate. People continue to throw out what is perceived to be trash with no earthly value and keep other things they believe have some worth. Most of us have an idea that coins, depression glass, painted china, art glass, postage stamps, and old books may be valuable.
However true rarities may not be apparent. Old product tins, paper advertising, old signs, and unidentifiable "what-its" may seem worthless when in fact they may be the most valuable part of an estate. Proper disposition of an estate is not an easy task unless the estate comes from a small furnished apartment, and then there may be a few rarities.
I recently witnessed an estate that was being thrown out on the curb and at night was disappearing quickly. There clearly are scavengers who know what they're looking for. That was a fair indication that something of value was being thrown away.
A few years ago I purchased two railroad posters from a flea market antiques dealer. Today the posters are worth at least $100 each, but the dealer showed me a third poster of "The Hindenburg" airship. The dealer said he found all three in the trash after being pitched by a family cleaning out a house of a deceased relative. The Hindenburg poster is worth hundreds of dollars.
Local libraries have a number of books on antiques and collectibles. If an item cannot be found, the state library system has an extensive collection that can be accessed through your local library.