I looked at your photos. Regardless of what the seller said, the viewfinder needs a cleaning. I'd have it done.
(I bought my present M4-2 in 2011 from KEH. It was listed in "Bargain" shape and turned out to be spotless other than that the viewfinder was dirty, needed collimation, lubrication, and adjustment. I had that done by my local technician, cost me $120, and the viewfinder was returned spotless, the focusing smooth and perfect. (He identified that the shutter could also use a CLA service as it runs unevenly at 1/500 and 1/1000 sec, but it's only off by about a third to a half a stop, not enough to worry about yet.))
These are old cameras and old cameras almost always need some maintenance. Unless the purchase price was way over the top, just have it taken care of and enjoy using it. 🙂
G