I search moparts,ebay, craigslist for ballpark prices. But recently I had a guy give me a set of aluminum welded valve covers for a 14x7 BB steel rim. Oddball rim of no use to me, I was going to send it to junkyard for 5 bucks.
I have a few friends that go on car sites but rarely post. So I end up posting their stuff for them or at least helping research their stuff and finding fair prices. I make nothing nor want anything to help them. If I feel their prices are out of bounds I usually don’t waste my time as it does take time. If you really want to sell something price it fairly and it goes pretty fast.