People are selling stuff on eBay to make a profit? Surely not!!
This prevents me to get a decent turbo card like the Blizzard 1230 IV for a reasonable price. I will never pay 150+ € for this one.
In about 2004, I sold one of these card for £290 (~375 Euros), which was about the going rate back then. They've actually fallen in price quite considerably over the years. Same for quite a lot of other Amiga hardware, actually.
The Amiga has a gradually diminishing fanbase, with a finite amount of hardware available. Over time, there is more hardware available per Amiga user. Not suprisingly then, prices are going down.
Having said that, I sold an Amiga 500 for £115 a couple of weeks ago.
I started at 99p with no reserve and just let the auction run. It went for what somebody was prepared to pay for it. That's how auctions work!