Knowing more about the Bear will help determine it's value, but in hte end it is what you are willing to pay and what the seller is will to accept. You can always check eb$y and get an idea of what similar bears sold for recently.
If you mean slowly flexing a bow with a stringer to check for cracks, stress, etc... I'd say it would be a good way to go...go slow and make sure the tips are seated properly...alot easier to look a bow over using a stringer than in your hand at half, then full tension.
Obviously, before stringing look the bow over carefully for cracks, stress, lifts, twists....check the tips...