People will pay outrageous prices for things on ebay because of the auction dynamic in place. It's more about "winning" the auction or item sometimes than negotiating a fair price. It's a great place for sellers, even though ebay's fees and policies have become downright draconian. Paypal then anally penetrates you after ebay is done.
Not a big fan of ebay anymore, but sometimes, commodity items are found there at better prices than can be found locally. Bought a HID headlight bulb for my car on there for about 25% of the price I could get it at the dealer or at Napa, Autozone, etc.