Used glass, checked element by element under a lamp before it is listed.
Haze, separation, fungus, and how the aperture blades behave when they are cold. Any of the four is disclosed in the listing with a photograph of the affected element.
We stopped selling C-grade lenses with front element haze. The saving is never worth the loss of contrast, and the pictures tell on it.
M42, Contax/Yashica, Minolta SR, Olympus OM and Nikon F manual glass, with the adapters to put it on a modern body. We will test the combination in the shop before you buy it.