Well, first off, a certain member will probobly pop on to call you out on your terminology any second now. Typically, they're refered to as Mosins, Mosin-Nagant, but never just "Nagant".
But, to respond to your questions:
1) Yes; the majority of rifles on the market with major vendors will all have been rebuilt by the Soviets post war. This does detract from value to some extent, however, given that the overwhelming majority are refurbished, this is usually expressed as a premium for non-refurbished rifles as opposed to reductions for your garden variety pieces. Non-refurbished rifles are available almost exclusively on the secondary market, and compare at a substantial increase in value; this is usually compounded by them being FInnish owned rifles, being an older model that was exported before the refurbs (ex, Balkan M91), or having some other interesting history in avoiding refurbishment.
2) Non-Import is typically more valuable.
3) Detractors are about what you'd expect - refurbishment, non-matching parts, sheer commonness (1942-1944 Izhevsk made rifles), etc. Factors which increase value revolve around dates, models, ownership markings (Particularly Finnish, it seems) and factory modifications; (ex, an M91 receiver converted to an M39 by one of the Finnish Arsenals)
A really good baseline reference is http://mosinnagant.net/USSR/default.asp and http://7.62x54r.net/MosinID/Mosinprimer.htm
This is all very general, but hopefully, this gives you a point in the right direction - I am certain that someone else will chime in with more detailed advice.
But, to respond to your questions:
1) Yes; the majority of rifles on the market with major vendors will all have been rebuilt by the Soviets post war. This does detract from value to some extent, however, given that the overwhelming majority are refurbished, this is usually expressed as a premium for non-refurbished rifles as opposed to reductions for your garden variety pieces. Non-refurbished rifles are available almost exclusively on the secondary market, and compare at a substantial increase in value; this is usually compounded by them being FInnish owned rifles, being an older model that was exported before the refurbs (ex, Balkan M91), or having some other interesting history in avoiding refurbishment.
2) Non-Import is typically more valuable.
3) Detractors are about what you'd expect - refurbishment, non-matching parts, sheer commonness (1942-1944 Izhevsk made rifles), etc. Factors which increase value revolve around dates, models, ownership markings (Particularly Finnish, it seems) and factory modifications; (ex, an M91 receiver converted to an M39 by one of the Finnish Arsenals)
A really good baseline reference is http://mosinnagant.net/USSR/default.asp and http://7.62x54r.net/MosinID/Mosinprimer.htm
This is all very general, but hopefully, this gives you a point in the right direction - I am certain that someone else will chime in with more detailed advice.
