@herman makes valid points about the reliability of selling price data. I look at the free information on hifishark and then most often list at a slightly lower price as suggested by @phd simply because I don't want to spend the time farting around with internet sales.
I am still not sure what problem this thread is trying to solve. People can list for whatever they want to and buyers can pay whatever they want to pay. It all gets sorted out eventually when the item is sold.