Good, close up photos of the right & left side of the firearm, the frame opposite the yoke, the back of the cylinder, the recoil shields, the left side of the grip frame, and the box are always helpful when helping a member determine if they are being presented with a reasonable price.
A serial number including the prefix, either S or N, would be helpful.
Knowing the cartridge would be helpful, .45 ACP or .45 Colt.
Knowing the exact length of the barrel, 6" or 6-1/2" would be helpful.
I think there are three possibilities in order of likelyhood:
1. This is a Model 25-2 in .45 ACP circa 1961-1977. If it was produced prior to 1968 (S prefix) and if it has original diamond center target stocks and truly has not been fired and is in the original "clam shell" (circa 1960-1969) box some would opine it could be worth $1500. More likely this is a N prefix gun made after 1968 and therefor would likely not have diamond center stocks and would more likely have a "Styrofoam bottom box with with foam rubber top insert" (circa 1969-1974) and if it were in unfired/like new condition with a really nice original box I would tend to agree with the SCSW (Standard Catalog of Smith & Wesson) citing a value of $1200 for ANIB (as new in box)
2. It could be a Model 25-2 in .45 Colt. All of the statements in section 1 above apply except you now have a more desirable firearm and a more valuable firearm.
3. The seller is wrong about it being a Model 25-2 and it really is a .45 cal revolver made in 1955 but this seems very unlikely.
There are some other