For a new in the box gun with a nickel finish, it would be a little high, for anything else, forget it. The Standard Catalog of S&W gave a value of $450 for as new in the box in 2006. I doubt the price has gone up that much since then.
The owner is either a) testing of there is a sucker born every minute, or b) he is looking at the MRSP of $919.00 for a new S&W Model 15 Classic on the S&W website. The problem with that is that per a poster on the S&W forum, S&W still don't have enough orders to justify the production run and the Model 15 Classic may not be produced. Which suggest that it is not worth $900 as even S&W can't sell them at that price.