The Python is considered the "Cadillac" of the Colt revolvers. It was originally designed to be a large frame 38 Special Target gun, but just be introduction in 1955 the management at Colt decided to chamber it for the 357 Magnum. It is a hand fit double action revolver that was offered with a 2.5", 3", 4", 6", or 8" barrel. The 3" is extremely rare. Available finishes were Royal Blue, Nickel Plated, Matte Stainless and Ultimate High polished Stainless. The Python was a catalog item until 1996. From 1996 to 2006 it was a Custom Shop gun. The demand for the Python is extremely high and sale prices of over $2000 are common. The current Blue Book values for a nickel plated gun are:
Add 20% for new in the box condition
Add 35% for satin finish nickel instead of polished nickel.
Add 20% to 25% for retail values.
I hope this helps you,
If you purchased it new and have not fired it, then it would be 100%. Slight use, less than a box of ammo can be 98%. Remember the books are a guideline and demand for a certain firearm can raise the price by huge amounts. A Python with a book value of $1200 may sell on one of the auction sites for $1800 to $2000. They were the best double action revolver made by Colt and are no longer made. The demand drives the prices way up.
It is close to impossible to tell what chamber has been used on a gun. Remember that some one trying to sell you something will tell you just about anything to make the sale. He may be correct in that it was test fired, but they would not load every other cylinder.A thorough cleaning like I do on guns that come in and you can not tell the difference from one chamber to the next. I can make a 30 year old gun look like it just came from the factory and I'm sure there are others who can do the same. The one sign of use that can not be hidden on a revolver is the drag line from the cylinder lock. It is normal for a gun, even those just cycled to check function to show the line around the cylinder. It should be extremely faint on a gun that has not been used. If you can supply a few pictures including a close up of the cylinder on the outside and both ends I will be happy to give my opinion on the condition. You can upload them by using the paperclip icon on the toolbar.