It seems that, no matter what rifle you have, there is always someone who chimes in to assure you that because of (insert whatever modification), it is worth less. The actual truth is, however, that the rifle is worth whatever someone will pay for it, provided you want to sell it. I am talking about proper modifications, not hacksaw jobs. Not so very long ago, Russian capture refurbs were scoffed at. They sold cheap. Take a look at the prices now. The days of finding a crate of like new WW2 Mauser 98's in a musty old gun shop are mostly over.
Each variation, model, change has its place in history. The "Finn capture" Mosin Nagants are a prime example. Not all are "captures", as a good many were purchased from other countries. The Finn rifles are an absolute hodge-podge of parts, upgrades, and show the resourcefulness of the Finn military and civilian armed groups. I have a 28/30 that stumped some of the collectors who belonged to the now defunct SCMNCA.
At guns shows, I always suggest to the budding collectors that there are three things to do: 1. Do your research, 2. Do your research, 3. Always have cash. No excuse these days for not researching. The internet is like having the world library at your fingertips.