The current private party sale price for an Interarms import Luger manufactured by Mauser is $1500 for a gun in 100% condition. 98% is $1200, 95% is $900 and 90% is $700.
I doubt there are very many above 90%, most will be 70% to 80% with a value of $500 to $600. I would pass on it, I believe it would be impossible to ever get your money back on it. There were many Lugers produced after WWII and imported. They will never have the value of a pre war gun. It will have Interarms or the name of other importers stamped on the gun which also hurts the value.