I only recall there being a screw, not a pin. Check the other side of the receiver in the same location to see what is there. My concern would be "What is holding the pin in place, and are original parts damaged?"
I have seen screws replaced with temporary replacements, they are used to help prevent damage when parts are reblued. A snug fitting pin would keep the recess from being dished out during the polishing process. Original screws would be installed before returning to customer.
On a rifle of that design and age a replacement buttstock is not unusual, but is it one that is Savage factory or one cobbled together in a garage. I would do a thorough inspection if possible before buying. A new stock, reblued, pin instead of screw...someone might be trying to hide the condition by showing bright and shiny instead, or it all could be legit. If the rifle has a square bolt I would look closely for cracks in the corners, I would also check headspace.
You have not listed chambering, make sure ammo is available.