Is your cartridge toast...maybe yes, maybe no??

I would like to question how we can determine the condition of our cartridges? Clearly if we are hearing significant loss of information or other damage on the LP being played, then that is probably an excellent indicator. However, many of us are probably using cartridges that are way past their prime, and yet they are still sounding just fine. Looking under a microscope wouldn’t seem to have much value, why...because how many of us know what the stylus is supposed to really look like...when new, when slightly worn, or when totally worn out! Can anyone really tell you what the true exact shape of a slightly worn out Shibata or Micro ridge or elliptical looks like? A completely worn out Micro ridge looks like...what? A brand new but damaged Shibata looks like what? I’m not so sure it really is possible to tell this with exactitude.
What about if the mechanicals are worn out, but the stylus itself is perfectly fine? How do we determine this factor...perhaps the cartridge will still sound good in our system, but the suspension or other mechanical parts are worn out!
I have posted before about buying used cartridges, and how IMO they are a pure gamble, but the real question now is ....is you cartridge toast, or is it just fine and your dealer wants to make another sale??
sounds great, but dealer says it is totally worn out...risk your records or buy another cartridge...new or used??