What is a typical life span of a stylus or cartrid

I'd pay the $70 to buy new.

You have no idea how the cartridge was played/(mis)aligned/dropped etc.

30 hours can be a lifetime if handled improperly.

IMO

Agree with Audiofeil, plus you have no way to verify how long the cart has been played.

It lasts until it's worn out which depends on use/abuse.

If it's a reputable dealer, it should have been taken care of properly. However, it it was demo'd by a number of customers not in the presence of the dealer, it could have been abused a bit. Personally, I'd pay the $70 and get a new one. It avoids problems.

If it were me(now that I know the price range): I'd buy a new unit(12% isn't much of a discount for used/demo gear). Still- I've never bought a cartridge(in the past 30+ years) without first inspecting the stylus, via a microscope. I've seen a number that were mis-aligned when mounted on the cantilever(new in the box), in that time. A lot depends on your trust of the dealer, and how much the $70 means to you. Can you believe his assessment of the time on the unit? Does he let cutomers mistreat his equipment?(unlikely, but possible). Like I said though- You should still audition the unit with your phono stage/pre-amp, before purchasing(new or demo unit).