Here's another pair of virtually identical cards. There's a helluva lot of extra room on top of the card on the left versus the card on the right, but it received a straight grade. Is that PSA 7 a 'natural' 7, or is it a PSA 9OC that was numerically demoted by a check of the 'no qualifiers' box?? There's no way to know.
(I would absolutely prefer the card on the right, because they are basically carbon copies of each other, so the 9 tells me it's perfect in every way, save for centering. The PSA 7 begs the question above to be asked.)
1969clemente50c.jpg
If you're viewing them on-line, there's no way to really tell unless there's big-time magnification available to study the corners, focus and such. Of course, if you're buying cards in person you can judge all of these factors for yourself, but the vast majority of purchases are done over the web, so (let the PSA jokes and insults fly) you have to have some faith in the actuality of the grade on the label.