I'm a little reluctant to buy 2nd hand equipment, especially lens, because I'm a afraid others are just selling the item because it is already 'damaged'. I know a lot of sellers are genuinely honest but there is still a chance that I may come across a dishonest one.
I just want to get some tips on how to inspect 2nd hand lens, what to look our for, what is 'acceptable' condition, what may affect image quality , etc.
Ex. my greatest fear is to get a scratched lens and don't notice it. will a scratch be always seen on the image?