War trophy papers

Can anyone tell me how much war trophy papers effect the value of a Luger? A guy wants to sell me a Luger he has with 4 out of 7 matching Ser#s. It is a Mauser with 70% finish, no pitting and an original holster with WW2 war trophy papers. The gun to me is worth $400 to $600. How much should I include for the papers? Thanks __________Mike