I have bought a few lenses before and asked the normal questions and checked for the normal wear. But when buying a more expensive lens like L lenses, ect. What are some more in-depth things you check or ask? Especially for older version 1 L lenses.
Normally I ask stuff like:
-Did it have a filter on for the whole life of the lens?
-are you the first owner?
-has it ever been repaired?
And I check things like
-scratches or fungus on the glass
-any wobble of any of the parts
-smooth and fast AF
-any damage to filter threads on the lens
What else do you normally check?