I was a DJ from '80 to '83, so yeah... Much more useful than a DVD rewinder.
The trick we always used to do was to hold up an album and look across its surface. If it was grey, then the grooves had been worn flat and it was time to get a new copy but, if it was shiny black, then it was still good.
I haven't owned any licorice pizzas for at least 12 years now... I was only able to sell about 250 back when CD's became popular (and made about $200 if I recall correctly), but the other 1,600+ were deemed about worthless and were given away to friends. Oh well.