I researched this extensively about a year ago when I was considering a "real" Mosin sniper purchase.
Overwhelmingly, my research led to me to the RGuns snipers. They have been thoroughly vetted, and authenticated as the "real deal" by guys that know what they're talking about (and I sure don't know all the "ins and outs")...and there are a LOT of counterfeits out there- far more than the genuine snipers.
It's all too easy to slap a scope on a 91/30 fudge some numbers and call it a "sniper".
Don't take my word for it. Do some research on Gunboards, and Surplusrifle forum.