I usually submit several hundred moderns to CGC each year for grading and I must admit that anything that comes back less than a 9.6 will be sold for a loss normally, unless it's a hot title, etc.
I purchase a lot of moderns each month (and I buy multiple copies of numerous titles), probably way too many and will go through the main titles and select the highest potential graded copies for submission. Any copies with slight dings, etc. automatically get reduced to VF or better for resale just to unload them at a loss.
Average cost for submission for a moderns w/shipping is around 17.70 per book, so I will submit multiple copies of high grade moderns that are relatively hot (Blackest Night #1) or high grade copies from the 80's. The 9.8's which I receive will be where my profit comes from, 9.6's will off set the few copies which I recieve that come back with a lesser grade (9.2-9.4). And yes, granted few and far between 9.9's and 10's can pay off.
I must admit that when I originally started submitting to CGC, I considered myself to be a good strict grader with over 30 years of collecting, but I was horrible at submissions as I would randomly pull bagged comics out of a box that I might have had 5 or 6 copies of and if the cover looked great I would send it in, that only took a few submissions and after I received a few 6.5 copper age books and looked on the back of the case and noticed manufacturing flaws, I made it a point to check copper/moderns especially close for any potential defects.
I have enjoyed this thread and would love to hear any responses. Also for my personal collection, I will keep a copy of the titles I collect that I receive back from CGC for my own collection and sell off the rest to help support my Silver and Bronze Age sets I am working on. Mainly Captain America 100-454 for now and I try to keep the Silver Age at VF or better in graded condition until I finish the set.