I worked at a Tech Hifi back in what I suppose was part of the "cassette era" (1978-1980).
We sold a lot of cassette decks along with the receivers, amps, tuners and turntables.
Nobody that I recall ever demoed a system using a cassette deck by choice to show off the sound. Cassette decks were demoed only when someone wanted to buy a cassette deck.
I do not recall anyone ever demoing a system with any pre-recorded cassette tape of the time. I don’t recall ever hearing a good one. Plus they were not made well and prone to jam.
We sold lots of good brands, Nakamichi, Tandberg, Akai, TEAC, Pioneer, KEnwood, Aiwa (these were very good and very popular back then), and others.