What's the best way? An economical way? When do you replace?
After how many hours of use should one check and re-check.
For 78s? For LPs For "Acetates"?
I asked this question a while ago on the 78-l list and was essentially told not to worry about it. My experience is that I can't see any wear on my styli with the greatest magnification I can muster even after thousands of records have been played.
The old rule for diamonds was 1000 hours. However this was in the days of ten to fifteen gram tracking force. Wear rates are an exponential function of force, so at the modern one to two gram range it probably takes much more than 10,000 hours to show significant wear.
Of course styli can be damaged. I always clean records and use a silicone treated cloth to reduce surface friction on records. Styli should be examined occasionally for possible damage, especially if used to play cracked or dirty records or if any change in the sound quality is noticed.