CBCS does have options to send a single invoice, however, it's pricey. It might be the same cost/book when factoring in multiple shipments (CGC) vs up-charge (CBCS).
Until CBCS actually fixes their customer service, I don't suggest anyone submits thru them. CGC, IMO, does a tremendous job of 'making things right'. A ton of people have problems even getting a response from Voldemort. Many times in my life I have been a repeat customer based on customer service. Bad service will always remove you from my consideration. It makes all of the difference to me.
I don't find any value in "verified" signatures. I simply can't trust them. I'd rather buy a raw book that a signature appears authentic on, than a graded book with someone else's opinion on the signature. That's just a personal preference, though.