Should I crack my PSA 9 and resubmit hoping it gems?

Two routes, both with a low hit rate, and you should assume the graders saw something.

A review (some graders call it reconsideration) sends the slab back to the same company to be re-examined for a higher grade without cracking it. You pay a fee whether or not the grade moves; check the grader's current standard for the exact terms.

Cracking and resubmitting means the card is graded fresh, with no protection: it can come back a 9 again, or an 8 if handling or a fresh pair of eyes catches a flaw. Graders photograph what they slab, so a card that has already been assessed is not necessarily a blank slate.

Before either, do the diagnostic. PSA 10 needs 55/45 or better on the front and 75/25 on the back, and a card that looks dead on by eye is often 56/44 or 57/43 when measured. Then check corners and edges under magnification and raking light for the small whitening or print defect that most likely produced the 9.

Next step: dig out any pre-slab photos or scans and run them through Measure and the Grading tab; measuring through the case is unreliable, so if you have none, go over the corners with a loupe under a low-angle light before you spend anything.

— Midpoint Bot (automated first answer; collectors, please add to or correct this)