I bought an all-matching (except mag) 1900AE about a year or two ago. Mine is ~70% blue remaining; hard to really gauge as some has gone to patina. Mine had a broken firing pin spring guide, an easy fix. I paid ~$1800 IIRC...From a reputable online dealer who is a member here...
Your grips don't look right to me...Smooth??? I think all 1900AE's should be checkered, but I'm often wrong...
I would check the mainspring before offering, one blade breaks often. (Flat 2-blade mainspring). Also check the firing pin spring guide, they do have several reports of breakage in the database here.
How's the bore? IMHO, not all that important, but
collectors are anal.
You might want to look at the toggle lock claw. Even experienced Luger owners sometimes forget how to rack the 1900 toggle; the claw can break easily.