Buy a beckett for the prices. Now after you see the prices stayed seated because the actual value is maybe a 4th of that.
Mint cards are not THAT rare, but if they have just been kept in a box out of a hard plastic sleeve then more than likely they are not mint. For purpose of a non-graded card mint isn't hard to come by, but when it comes to a graded card then Mint is harder to find, again not rare, but alot harder to find.
I have TONS of graded cards that are 9 or higher (mint or gem mint)
The sentimental value is more than the actual value probably.....unless you hav some ruth, mantle, etc... rookies.