Stamp Questions.
 

I'm new at stamp collecting and have a couple questions.

Using the prices in the Scott Catalogue as a starting point to guage the
value of a stamp, I was wondering what corrections to apply in the following
two cases.

I was wondering how much someone discounts the value for a mint stamp
because it is hinged? Does the fact that it might be a Light, Regular, or
Heavy hinge have a significant impact on the general percentage adjustment
you make? I do understand that early issues as noted in the Scott
Catalogue are listed as a hinged price.

The second question is about CTO stamps. How does one figure out what they
might be worth by using the Scott Catalogue. It is obviously a 'used'
stamp, but is it worth as much as a used stamp that really went through the
mail? It is worth more, or less? Again, what general rule of thumb
percentage does someone apply to come up with a value?

The third question is: How do you put a stamp that peels of
into a stamp album? Do you just leave it on the paper it comes with, or
can you put is on a piece of glassine?

Thanks.