To buy or not to buy a used cartridge?

No big problem. Most owners from expensive cartridges are very careful and you can ask for pics. when the cantilever is straight and the suspension not down, then it is fine. Never had a problem. Probably I had luck and met always the nice guys...

I've bought 4 used cartridges here on Audiogon over the last few years. All have been as advertised or better than expected. I always TALK to the seller. I find out about their equipment, LP cleaning, listening habits,etc. Then get a feel for their honesty/openness.
I believe anything you buy used has some sort of risk. Just need to feel comfortable about item and seller before you lay out the cash.

I have mixed feelings about this also.

I agree that this is probably the one item that I would consider being a risky purchase, if buying used. There is just so much that can go wrong buying a used cartridge.

However, that being said, I have bought three used cartridges:
A Dynavector XV-1S from a friend, (okay, that was a pretty much a safe bet),
One from a guy on Audiogon, (A Shelter 90X, which was in very good shape),
And even one from a guy on Ebay, (which while it did make me nervous, the Koetsu Rosewood Signature was in near mint shape). So, all things considered, it was a great way to save money. (I bought these for about 30-35% list price.)

If you deal with a person who you feel comfortable with, (especially if you've spoken to them, or if they post a lot here or on Audio Asylum), then you can probably get a decent deal. Buying from an unknown entity is likely to make for an anxious buying experience, but not necessarily a bad one.

My two cents worth.

I have brought 3 used cartridges and have not had a problem. All have come from audiogon and have been from people that frequently post. Not sure that is a guarantee but most on this site are into the music and gear and not about screwing the uninformed or novice buyers. If you go to ebay or others, good luck. that imo would be a crapshoot as there are a lot of unreliable sellers on ebay

I have bought literally dozens of used cartridges, and while it is an extreme risk because half are no good, the price is right, and often there are treasures that compensate for money wasted on the others. All you need to know is that you will get stuck half the time. To me, that rare jewel is worth the risk, though.