I think everyone has an idea how CGC grades BUT there is still a grouping that don't care a thing about CGC. They don't submit, they don't buy graded books and they still sell a ton of raw books to folks that feel the same way.
And to be honest I don't feel that is necessarily a bad thing as long as they are consistent in their grading and pricing and you know what you are getting. If you know Harley's 9.4 raw is only going to be an 8.0/8.5 CGC then it shouldn't be purchased in the hopes it can press out to his assigned grade.
For me personally, when CGC first came along I spent hours and hours and submitted hundreds of books to learn how they graded and what counted off. A lot was pretty surprising because at that time I never even thought about some of those deductions on high grade books. It made me pretty successful at submissions but that's what I was looking for at the time.
Some people adjust to change well, some not at all and some go along just enough to get by. I think as buyers we have some of the responsibility to know how someone else grades and then just be aware of that when we submit books.
There's a lot of guys out there that are really fair though and easy to work with so I'll continue to buy from them just for that reason.