I would trust a seller with many posts, especially related to vinyl reproduction and also many feedbacks. Moreover, the hours should be in the lower end, like much less than 500 hours, unless it is something like a super duper High end cartridge with specific magnetic designs that cost $$$$ and perhaps the retipping cost more than justifies the used bargains you are getting. Moreover, people who usually sell very high end MC cartridges tend to have a couple laying around, which means that whatever cart they are selling usually have been used sparingly.
Nevertheless, I would look into some web vendors. I scored a quite expensive low output MC from a famous Japanese manufacturer brand new in the box for about 50% less than retail due to a mistake that was made in advertisement. I was looking into scoring an extremely low mileage entry level cart from the same manufacture but it was "Sold" so the owner graciously sent me the next most expensive cart in the line, brand new in the box for the same price!
Good luck with the hunt.
