I know most who are on here love cassettes for the music they contain, their retro appeal and the hands-on aspect of owning something physical.
There may be some who are interested in the technical aspect - how to make a good recording and what old blank cassettes are worth looking out for.
To that end, take a look at this video and associated YouTube channel: Cassette Recording Basics - A Crash (and burn?) Course - YouTube
If you spot a batch of tapes on ebay and wonder whether they are any good, then Cassette Comeback has likely done a video about them.