These are a general guideline for determining value, based on what dealers are selling instruments for at retail. By looking through several different magazines dedicated to the vintage guitar industry, you can get a general idea of what things might be worth. There is a fair market value for everything. Based on what other dealers are selling instruments for, and given the differences in geography, this all determines a price. Now you may see variations in what things are listed at in different dealer's stocklists, but there are several determining factors that dictate price.
Condition always effects price.
An original clean instrument will bring a far greater price than the same guitar that has been refinished or repaired. A guitar that is rare or one of a kind will also bring a greater price than the run of the mill instrument. All things considered the more unique the instrument, the more it might be worth. With so much to take into account and all the variables that determine what something is worth, it might be to your advantage to get some expert advice when trying to sell a guitar or amp. If you plan to sell your guitar to a dealer, remember that dealers buy at wholesale and sell at retail.