I have an old dictionary. Will you buy it?
Merriam-Webster maintains a large library of the dictionaries and other reference books the company has published over the course of its 150-plus-year history, and it does not need to expand that collection, so the company does not purchase old editions of its books.
The value of an old dictionary can vary widely depending on the condition of the book, its rarity, the demand for it on the used book market, and many other factors. Merriam-Webster's expertise lies in creating new dictionaries, not in appraising the value of old ones; the company cannot place a price on past editions of its works. A used book dealer or perhaps your local public library may be the best sources to consult as you begin to research the value of your old dictionaries.