Did some digging (which I should have done first, lol), and found that you determine the Fair Market Value based on current sales of the card in it's current form (ungraded), and an approximation of what is found should work for the "value" of the card.
Also, if the card is deemed to be worth more than stated on the submission form, the submitter will be charged for the tier in which the card should have been submitted.
If all that sounds correct, would appreciate someone with more experience than me (which would be any, lol) to confirm or correct?
Thanks!