Experience purchasing a used high-end cartridge

Trust but verify.

I am saying that inspection by a competent disinterested professional third party is what I would require if I were to buy a pre-owned megabuck cartridge. Speaking for myself only. I guess you don't agree, and that is fine.

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.

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

I don’t know how anyone else’s experience could bear on your decision, unless you unearth another person who bought an LOMC from the same source. If you’re really insecure, ask the seller if you can have the cartridge inspected by a trusted retipper, at your expense and in advance of any sale. If he doesn’t agree to that, you may have your answer. If he does, you’ll know exactly what you’re getting.