As a parenthetical comment, I've often wondered why it isn't more common practice for the sellers to get an appraisal and then use the appraised value as the list price. Kinda like I've done with cars - look it up on KBB and then list it for that price. Perhaps with some adjustments for how desperate one is as a seller, or if there are some things that the appraisal doesn't include (a new school being built nearby next year or something like that).
I'm sure there are reasons, but it's something I've thought of doing as a seller myself before for various reasons.
Considering a typical appraisal might be $400-500 it seems like a worthwhile investment when you're about to pay a realtor thousands or tens of thousands of dollars. I used to be a commercial real estate appraiser and was active in a forum with mostly residential appraisers and the anecdotal evidence was very few buyers were will to spend a few hundred dollars for an unbiased opinion.
My guess is that the thousands of dollars a realtors 6% commissions represents isn't "real" money they have to pay out. It just comes out of the proceeds of the sale. Whereas writing a checking for ~$400 is an actual cost.