Indeed, but I've also noticed that a lot of the sales for stuff I'm interested in are "buy it now" type. And I have no good gauge for what a price "should" be, but for instance I'm willing to pay a couple bucks more for a chainring of some odd bolt spacing, that prevents me from having to buy a whole new crankset.

You can search for sold listings to see what price an item has recently sold for. It’s not that useful though for rare items that are not in frequent demand.

Part of the reason the “buy it now” is so popular is as a seller sometimes buyers make an offer for an auctioned item then once you refuse they bid up the price so they win but then they don’t transfer the money.