This could be a Pre-18 (Non-Model Marked 4-Screw), a model 18-no dash, or an 18-1. All of which are desirable, but due to rarity, worth far different amounts.
Much depends upon the marking inside the crane cut out seen as "MOD 18" and the serial number.
I collect K-22's and do not have an 18-1. Like most -1 models they are tough to find in any condition.
If the gun is all origional (grips, finish, configuration) and the 95% condition estimate is accurate $499 is just a little high for a Pre-18, good for a 18-no dash, and about half what an 18-1 would bring. Unless of course the gun has the correct origional box serial numbered to the gun with tools and paperwork, then it's a very good buy in any configuration.
Good luck!
Drew