It used to be that one could fairly reliably price a book by taking 25-35% off of the abe price. Then it became 25-35% off of the abe price excluding the ridiculous outliers. Now it's evolved to you cannot do this anymore. How does one convince a seller consulting abebooks that 80% of the listings are outliers? By definition, they aren't, even if they are not reasonable.
I had a mild run-in on an ebay sale some 5-6 years ago and they cited prices on abe as to how I got a great deal on a book that had significant foxing. I tried, but could not explain to the them to the point of actually getting through, that their argument held no water. To them, their argument was firmly ensconced in a refinished swimming pool that was only held together by the fresh coat of paint.