Somehow "refinished" brings a bad tast to collectors. Especially if we talk about US made guns like Winchester, Colt, Marlin etc. I still remember I had a Colt Lightning Baby Carbine in .44wcf with British proofmarks and it was refinished. Nobody wanted even though 99,99999% of the original gun was still there and in sharp condition with rifling, action, wood, markings etc.
The collectors marked is also a speculative marked, which is influenced by business cycle and moods.

As for your Mauser Model A. How many will you ever find?. They are not like some Winchester models that were made in the 100000-1000000s of. Continental & British made hunting rifles/shotguns in general doesn´t suffer a priceloss when refinished as US made guns if you are thinking in investments. If you like Mausers in general that refinished Model A will do you good and in the gun is in overall good condition where you can do hunting/shooting throughout your life well into the next generation. You don´t have to worry about a tiny nick/scratch and you "investment" have dropped 60-80% of value.
Some guns is so rare and desirable that if they show up you better not pass up refinished or not. That Mauser Model A in refinished condition is still a Mauser Model A. It will never become a LC Smith or Mossberg. Buy it if you like Mauser.