This is a quite unusual eBay stance, almost contrary to their neverending assault on the common seller that has rendered selling on their site an exercise in frustration. While there are unscrupulous and deceptive eBay sellers, at least we as the buyers have a choice when purchasing to ask questions, review feedback and pictures, and select a properly described item.
When dealing with raw items, I can see how returns can be problematic however. Even with CGC grading, flaws can be graded very subjectively. Even a high resolution scan and a close-up picture will fail to illuminate minute flaws only visible to the naked eye under proper lighting conditions.