What are 50 years of service disabled American veterans 6 cent stamp worth?

Answer 1

This is an example of a minimum catalog value stamp. Its catalog value is 20 cents if mint and 20 cents used. A pair which includes its "twin brother", the POW stamp catalogs for 30 cents mint.
When most US stamps come out they are assigned a catalog value of 20 cents for used and twice face rounded to nearest nickel for mint or 20 cents whichever is more. Most of the US stamps issued in the last 60 years are still at minimum catalog.
The catalog value is a guide to what a dealer charges for this stamp in an individual custom order for it. Most of this price is to pay the dealer for the labor in locating the stamp in his stocks, replacing it when it is sold, and making up the order. Most of these stamps are sold as part of a packet or collections or mixes of 100 or more stamps for 1 to 2 cents each if used ,and face or less for mint.

After buying a number of such packets or mixes, a collector usually finds that certain stamps are missing and then he may place an order for just these particular stamps in order to complete his collection and pay close to catalog value for them.

Dealers buy used minimum catalog stamps in large lots , collections or accumulations. They do not want to buy such stamps one at a time or in small lots. They pay less than 1/2 cent each for them. They get their mint stamps from the postal service at face while they are available and buy up accumulations of mint stamps for around 80% face . So, if you just have a few such stamps to sell, your only hope is to find a collector who just happens to need that stamp for his collection. If the stamp is unused, you can use it for postage at its face value. I should add that if the stamp is defective in any way, it is worthless if used.