The Mauser advertisement you found on facebook has nothing to do with the pictured rifle.
It also has nothing to do with the soldier and rifle pictured, who actually looks like he is holding a Mauser ES350B.
To determine more information about the rifle you need to remove the stock from the barreled receiver and take a picture of the proof marks located on the bottom of the barrel. The rifle is a post war commercial rifle, built from recycled or left over K98k parts. These are sometimes called "cigarette guns" or "guild guns" though this is a misnomer.