I think your revised logic is fine, but my only criticism would be that it depends on the level of comic knowledge a "buyer" has. The more informed they are, the less likely they are to buy the grade and not the book.
However, if you have that much money - does it really even matter...
That's the point of my revised logic. The players that play in this pond would want that book even if it is over graded. It is still a heck of a book. That said in any auction, if two are ready to tango, the action begins.