Experience purchasing a used high-end cartridge

There are a number of good re-tippers out there,  many original manufacturer have rebuilding services. I would not worry too much specially if the price is reasonable so when you add the rebuilding cost its still a good price.  

I recently bought a Sumiko pearwood celebration 2 at well below 50% cost, its sounds great and at the price i can rebuild it and still be below the used price market. 

Like I said, trust but verify with an independent expert.  I'd go that route without a second thought.

I know of a couple of folks that have done this and enjoyed ridiculously good cartridges for a time and then resold them.

I don’t consider myself paranoid but would not even consider it. When I was 18 I  got completely ripped off in the purchase of my first used car… once burned… And absolutely every friend that I lent a thousand dollars or more has never paid me back…

trust but verify with an independent expert.

In other words, distrust until verification. If you find a seller willing to let you ship his cartridge around and have it handled by some third party, sure go for it without a second thought.

If you are inferring that there is some risk to the seller, I would think not, if you both (seller and buyer) choose an inspector who is well known to the audio community and with an impeccable reputation, like Peter Ledermann, etc.  Or even better, perhaps the seller has particular experience with one professional retipper that he or she would prefer to use.  Possibly also Wally Tools does pre-purchase inspections of this kind. It's well worth the extra cost to the buyer, if we are talking about a cartridge that costs thousands of dollars.