It is a bid odd as we associate that with salesmanship, but on the other hand it is also a bit of a conceit in our hobby to play with number grades like its a science, which it surely is not. Sales are largely subjective, how people feel about the book's intangibles, its eye appeal, for example, is in the eye of the beholder.
Agreed. We all operate within the illusory construct of CGC's purported objectivity when, ultimately, the process is that a grader looks through a comic, shrugs and writes down "9.8", which then sells for twice as much as a supposed 9.6. But it is a fun game to play.