Selling used equipment can be depressing when the seller can't get the price they want, but some pieces are selling fro stupid money, even though they were nothing special when they were new. Audio Karma is one reason- some of those people are absolutely in love with stuff that was mediocre, at best and sometimes, it was crap. A Pioneer isn't worth >$1000, but that's what they're selling for. A Teac cassette deck isn't worth more than $50, but I have seen some going for hundreds. I never liked those Tascam is a different story, though.
If you like what you find and don't have a problem with the price, consider it. It's a good idea to do some research about whatever you're considering, too. Things like, "Can I still find output transistors for this after 30-45 years?", "I found output transistors, but they're really expensive", "Does it need proprietary parts?", "Where can I find a second replacement tweeter? or "I need a special part for this open reel machine" can be a problem, after the sale. As an example, if you decide to buy a turntable and happen to like the sleek styling of Bang & Olafsen, don't expect to find a new old stock cartridge for it. They stopped making those decades ago and the ones that are available are very expensive. Some of the cartridge models are being rebuilt by Soundsmith in NY, but they're still not cheap.