eBay takes a 13%+ cut, then there's shipping, so you're looking at $300 after cost of business. If you're selling a lot, sure, capture that $100 difference. If you're selling one and dealing with buyers, you'll spend at least one hour taking pictures, writing the ad copy, doing client management, going out to ship + gas to get to the post office, risk of buyer return/fraud. Say you're worth $50/hour and you're being very efficient and do all that in one hour, you may end up with a net economic gain of $40-50 after all that. Is it worth it?
Whenever I sell used good, I use ebay to set the price, but I sell locally, so there's no shipping/fees involved.
Local prices around me always seem weirdly high - I sort ebay by cheapest price+shipping, match that, and that usually puts me cheaper than 90% of local listings and gets me plenty of interest.
TBH I'm not clear on why anybody outside of rural areas is selling on ebay for non-niche things.