I look at auctions for microcassette-related items on eBay every day. Yesterday I saw this one:
The guy is selling a Radio Shack brand recorder and 90 microcassettes for a starting bid of $0.99. The microcassettes all contain secret recordings made by a previous owner of conversations and telephone calls. What a treasure trove! The seller includes a YouTube video in which he describes the items and even reads texts from the j-cards of the microcassettes. It is a shame that he didn't play excerpts from the tapes!