Card Grading defects
 

I’m always perplexed at some of the grading on cards from third parties. I can’t figure out what is the worst defect to devalue a card?

Stain? Paper loss? Markings? Trimming? Major creasing?

Thanks.

Amongst your list, trimming is easily the worst. It's a figurative felony, while the others are misdemeanours. Trimming means it can't get a number grade.

After alterations (trimming, recoloring, rebuilding, etc), cards with pinholes will get a Poor 1 from PSA if the card wasn't designed to be stapled onto something (like matchbooks, carton cards).

Interesting.

The Gretzky Wagner T206 was graded PSA 7 but was trimmed. Does PSA ever re-grade cards after more info available?

Wagner was graded PSA 8.

The Wagner shouldn't/shouldn't have received a number grade.

Altered cards should nor get a number grade
 

As previously stated after alterations which are supposed to prevent a card from getting a number grade the next worst flaw is a hole of any type pin, nail, staple, whole punch, etc, automatic 1 or 1.5 depending on company.

Yes, PSA will recall some cards that they've made errors on and pay the owner the difference in value between the old grade and the new grade. However, the owner needs to agree to the process. Obviously, none of those owners would rather have the cash difference and a PSA Authentic Wagner.
There were threads here in the last week about a wrongly labeled T206 and a Bench rookie labeled Venezuelan that was not. PSA is fixing the Bench because the auction house sent it back to them.

A piece missing, depending on size, can be worse than a hole. (not my hand or dog)

LOL...I was just about to compliment you on your choice of nail polish!

Correct
 

but then it doesn't even get a number so i disqualified it from the discussion. :D

I think on a good day ole Large Ass Herzog could get a .5!! He only has a flesh wound and for around 109 yrs old that isn't too bad. Alas it is AUT for him...and from a more recent photo op, which he always enjoys.

Ultimately, it’s sort of arbitrary. To me, a card being very off center or having poor registration/focus is worse than a speck of paper loss on the reverse or rounding of the corners. But the latter lower the grade much more than the former.