Applications and websites to learn about stamp's value

Greetings saber
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The most surest way to find the value of a stamp is checking with a Scott Catalogue. These catalogs cost a lot of money themselves, thus the best way to use them is checking them out of your local library.
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Now, the minimum CV (catalog value) is $0.25. That is the amount a qualified stamp dealership would charge for selling a minimum valued stamp. Ninety-nine percent of these dealership reduce the selling value by at least fifty percent. Folks who are not a qualified dealership would be able to sell a minimum CV stamp for two cents. For stamps that have a higher CV the real value of the stamp is somewhere between 25% to 75% less.
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I hope this helps you.
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Respectfully,

Gordon Lee