New or used cartridge

I have have good experiences buying a previously owned cart in the past, but have heard several telling me to buy new..  I wish there was a way, to tell how many hours was on a used cart.  Other than putting the cantilever under a microscope,  I see no way concerning the hours/use/condition of a used cart..  I kinda look at it as buying a used car.  Let someone else take the initial "hit". then buy from them, as they're moving over or up.  I have an excellent Koetsu Urushi Black I'm going to put up for sale.  I love it's sound, but am wanting to move up the ladder so to speak.
Please give me opinions concerning this.