Its impossible to prove a K43 with a scope is an original dedicated marksman rifle, unless numbers match, on the numbers on this one don't appear to match. But nto all scope mounts got numbered by this time late in the war, and many were added in the field as all K43's had the scope mount fitted in the factory, so a scope of an original could be taken off in the field and just slid onto another K43 and it would work (as per the ZF41 on the K98k)
The 'ac' code on this rifle show it to be a Walther made K43, and the scope code 'ddx' shows as being a Voigtlander und Sohn made scope, so they are the right combination of makes for a real sniper K43, as in general the Mauser made K43 snipers were all fitted with Voigtlander und Sohn scopes, whereas in general the BLM made rifles used 'dou' made scopes.
As to value, I would have thought as it is, anything from $3,000-3,500 upwards would be my very uneducated guess?