Well then you'll be glad to know you did nothing wrong. Firstly, you can't prescreen for a 9.9 and prescreening for a 9.8 does not mean it can't get a 9.9 either. Prescreen means they only slab it if it is "at least" whatever grade you inscribe.
So you did nothing wrong there. If your book is a 9.9, you'll get a 9.9. Also, I didn't understand. So you did send in 25 books with 9.8 prescreens? And opted not to have them pressed?
Also, as for you question of being scared for an outside party to handle your books incase they lose them, your book has as much chance, if not more, of being lost at CGC or CCS (the company CGC uses for pressing). That's why they ask for the value your comic is insured under. And you can look it up, books have been lost and that insurance money had to be paid out. So if you were ok with CGC, then you'd be ok with an outside presser who has a lot more riding on their trust/reputation than CGC does. If CGC loses your book, big woop, they wont go out of business. But someone who presses for a living has a lot more at stake. There are a bunch of competitors, at similar costs. All they need is some bad reviews to go down and never be used for pressing again.
So yeah, reputation is their bread and butter, hence why I was perfectly fine sending in a $900 book to be pressed (among many other books). If you want more info on my presser, send me a PM, I will be glad to recommend.