Just had to add my recent experience to the thread. I have not used CCS in more than 3 years because I wasn't happy about the results. Since then I taught myself to clean/press and I am pretty good at it and the resulting grades back that up. I've been able to upgrade books I cracked at home and raw books come back with great results too. Now, why would I use CCS again recently? Well, I had two books that I bought based on the grader notes hoping to bump them. One of then (9.4) had an indent on the front cover that I could sort of see with grader notes stating the same, and the other (9.2) did not look pressed at all with a stacking bend, some spine ticks and some dirt on the back cover, but no grader notes.
These are bronze age books that I would normally take care of myself, but I was curious about having CCS have a crack at them, and I felt sure that the defects were definitely pressable and just maybe I had a better chance of getting those bumps. I fast tracked them too. Unfortunately, the book with the indent came back same grade (9.4) with grader notes still saying there was an indent on the front cover - ok maybe I was wrong, the indent was not pressable. Maybe. The other book that clearly was never pressed came back same grade (9.2) but went from white pages to off-white to white.
I am going to chalk this up to a bad decision on my part, but I do have to note that the reason I stopped using CCS a while ago was because the pressing just wasn't any good. They didn't press out what I knew then and know now is pressable. Comic book condition and defects and all the rest is subjective of course, and even though I own officially thousands of CGC books (don't remind my wife) and I have been submitting/cleaning and pressing for a bit, I am no expert, just someone with more experience than the average bear. However, I can't help but feel that I wasted my money on a service that I should have known was going to disappoint. No I won't use CCS again, doing it myself works out way better. I just had to remind myself of that.