Are 500 hours too many for a used hi-end cartridge?

The only used cart I ever bought was when  starting to assemble my first high end system and looking to save money, being fresh out of college.

 It was a Spectral cart (anyone remember those) that i bought on Audiomart newsletter and the entire assembly was tilted. The seller didn’t want to return the money and I think settled on refunding half after I got the owner of audiomart involved. My bank had told me incorrectly that a bank check (or certified, I forget) could be cancelled. I confirmed it several times and was always told yes. When I tried to cancel the check, of course it wasn’t- but my bank paid off anyway since I had people’s names that told me the wrong info.

never bought a used phono cart again, but also bought many used high end gear and never had an issue other than that once.

incidentally my strain gauge cart has many thousands of hours and now I want to have it checked .  Sounsmith was quoted saying a strain gauge owner put 6000 hours on listening to vinyl all day long, and after sending back to Peter to look at under a microscope, the stylus still was not worn out.  Sounds crazy, but Tam henderson from reference recordings claims he plays test lacquers with the cart and they don’t wear out! 

1. no, most quoted low hours tend to be vastly understated, reality without documented proof is a guess at best,
2. yes, cartridge components deteriorate over time, with or without use,
3. yes, see 1.

:)

I use LAST Stylast on my Denon DL-103R/Audio Musikraft cartridge.  I'm about 400 hours in and there is no discernable wear to the stylus when examined under 100X magnification.  All my LP's are treated with LAST Record Preservative.  So I guess I'm happy.

Great information Chakster on stylus life and I love the toothbrush analogy. 
I agree. A new ART 9 would be a much better choice than a used cartridge. 
1st off we are terrible at estimating usage and there is a tendency to minimize this. If you asked me how much time I have on any one cartridge the honest answer would be, "I have no idea." It would be better to go by the original sale date. But still this does not indicate the condition of the stylus as it depends entirely on record hygiene and tonearm setup. Buying a used cartridge is a crap shoot. If the cartridge were less than 6 months old and had not been damaged I might consider it otherwise it is better to stick with a new cartridge. A note on re tipping. This is best done by the original manufacturer. A top of the line cartridge will cost more to re tip than a middle of the line cartridge costs new excepting perhaps Soundsmith.  Last "preservative" does absolutely nothing. It is 100% Freon ( a type of chlorofluorocarbon) think brake cleaning fluid. It is a great solvent with a very low vapor pressure (evaporates almost immediately) It's best use in audio is to clean tape heads. 
Very minor changes in the shape of a stylus are extremely hard to see under a microscope. I examine mine all the time at my office. Once wear is visible you are certainly at the point where you are chiseling your records. Is wear before this occurs audible? I sort of doubt it as the distortion occurs at very high frequencies. People my age certainly could not hear it. So I do believe watching for flat spots is useful. Once you detect this it is time for a new cartridge or stylus. I have been meaning to try a USB microscope as I hear they are useful for this and they are quite inexpensive.   

If cartridge aging is an issue, then y'all need to know of this guy, who does phono cartridge repair and retipping.

http://www.phonocartridgeretipping.com/index.html