Finn M1891 for 149.00 but have questions

Went to a gun store today that carries usually over priced mil-surps and as I walked in I noticed the distinct muzzle of a 1891 sticking up. A quick look revealed it to be a finn captured with a finn stock and sling hangers. Stock was in great shape but 95 percent of the blue was missing. Appears to have the original sights etc. What confusd me was the receiver markings or mainly lack there of. Receiver was blank except for a tiny SA in box three serial number sets two of which were lined out, two large S that appeared to be part of the serial numbers? Finally by it's lonesome was some type of eagle stamp in the center of the top receiver flat but I am not sure it was Russian. Anything odd about the rifle that would make it unusual? Given that it is an intact decent 1891 that I can get most likely get for 125-130.00 OTD I think I am going back tomorrow and put her in layaway. Sorry to pester with what is what I believe are routine questions but I walked away from Mosins a while back and cannot get to my Mosin collector's book or either of my 1905/06 Finn captures to check the Eagle mark. I know some 1891s were "sanitized" but I thought this was when they were remanufactured/rebuilt into entirely new rifles like the m39. Again no where the mosin man most people here are but the basically sanitized receiver and lined out serials threw me for a loop as I don't ever recall seeing one on a 1891. Again any and all help is most appreciated.