Do you buy used carts/needles? Is it risky?

I would highly recommend used cartridges. 
As mentioned know who you are purchasing from. 
i usually try to exchange numbers and talk direct. 
 

I purchased a Hana Red this week. 
it came as advertised. 
I paid 1/2 of the new cost. 
could not be happier. 
Good Luck 

I love buying used. I've bought new too, and that can be OK with discount - but I've never needed to file a warranty claim, and don't expect to. Buying used on USAM or Audiogon really isn't high risk, with a few simple guardrails. The guys selling $3K used cartridges generally aren't the same kind flipping a 1990s Corolla or PlayStation on Craigslist. Look for a straight cantilever and signs of corrosion. Sure a guy could lie about hours, but I suspect most of us are conservative on estimates and fall on the honest side.

@viridian I was eyeing the Nagaoka  MP-500. If I may ask please, why do you not recommend it?

I buy a lot of used gear. The only exception is a phono cartridge. You have a nice table so why would you cheap out on the cartridge?

In the end, you will never know how many hours are on that stylus. Pass.