I don't know why members keep obsessing about these listings, they never sell. It's not only boomboxes, there's many listings on eBay for all kinds of things whose pricing logic isn't rooted in reality. I often see used things for sale, well worn, and then in another listing next to it, a brand new one, with FREE shipping being offered for 1/2 the cost of the beat up one. With warranty! Obviously, anyone who doesn't bother to check prevailing prices and willing to plunk down huge change for something whose price exceeds any logical utility deserves what they get. I could see someone overpaying for a nail, hammer, anything that has utility simply because they "need" it at that particular point in time. And when I say overpay, I'm not talking about $10k for a $700 item, I'm talking about paying 20-50% higher.
Years past, I sold some RJ45 wall mount receptacle plates on Amazon. The price was in line with what you could get them for at the big box stores. But the shipping charges were outrageous. Instead of combining the shipping charges, amazon charged the buyer shipping/piece. In other words, 5 panels = 5x the shipping cost. I was fearful buyer would balk but the shipping address was for a home theater installation company and they paid it. I surmised that they probably couldn't get these locally so they were willing to pay whatever to complete the job they were doing at the time. However, there comes a point where pricing exceeds utility at which point, you are paying collector pricing. Would a rare coin collector buy a high priced one off eBay without doing some due diligence first to see if the price is in line with what that particular coin, mint, condition, misprint would fetch in a "reasonable" market? I don't think so. Someone might buy a $2 screen protector for their phone for $5 and be happy. I can't see a scenario where anyone would be happy with a used $10,000 boombox without knowing that this is where the market price is for one.
Why list like this? Simple. eBay offers monthly "free" listings, depending on your eBay status. For example, a member might be given 50 free listings/month. These cost the seller nothing (unlike earlier days when listings cost money to list so you would be tossing money down the drain if you listed to not-sell). If it sells, the seller wins the lotto. If not, no skin off his nose.