Cartridge new or used ?

I have some questions for all of those folks who buy used vintage cartridges, or used non replaceable stylus cartridges...
how do you know the condition of the diamond? Do you look online and get a generic picture that may or may not correspond with the stylus shape you are expecting to see, and are you able to actually view all of the facets of the diamond..on all sides, or are you doing something else? Using a high powered microscope? Are you able to determine the exact cut and angular correctness of the facets? 
Some other method to determine wear and condition? Do you have any idea as to the condition of the suspension and what that is supposed to perform like...or do you not care about this aspect that much, and assume all is as it was from the factory originally?

@chakster 

I don’t know who was responsible for the 80’s AT cartridges, but maybe their customer service department may be able to help. 

Ya pays ya money, ya takes ya chances. Glad to hear others have had good luck with preowned carts.

You can minimize the uncertainty of the "takes ya chances" part with a dose of healthy common sense and  research.

As I have said it is NOT for impulse buyers or the faint of heart...lol.

Works for me and keeps my pocket a little fuller each time I buy a used cart.

Good luck to all.