Can I narrow it down to just the top 10???
How about the one that caused me to stop grading with them for 8 yrs. Sent in a Batman Adventures 12, purchased on these boards, definitely a 9.8 candidate. Comes back 9.0 with a crunched corner. Thankfully I know Matt Nelson, come to find out that cgc dropped the book, graded it, and never even told me this. Had to resend it to Matt to at least have him press/resub it to a 9.4. Then had to argue to get credit back for the diff in grade.
CGC if you're reading this, you're slipping BAD. I've been grading since day 1, hopefully you get your act together, hire more people as needed, and remember that your customers are worth more even though you don't see that right now.