The single warhammer of the sniper shot card says, "you hit for critical damage." I am not sure how I am supposed to read this. Does this mean that you hit, and every wound that the attack would normally cause is considered to be a critical wound? Does this mean that you hit, and cause critical damage as if you had rolled enough boons to cause critical damage (thus causing only 1 of the wounds dealt to be a critical)? What happens if you both succeed and roll enough boons to invoke critical damage? Would someone mind clarifying this card for me, because last session I (as the GM) pretty much had to make an on the spot ruling, because I am really not sure what that sentence is supposed to mean...

When a card says you hit for 'critical damage' it means one wound is converted into a critical. It is exactly the same as if the card said "+1 critical".

I belive this is explicitly covered in the FAQ (if you're looking for the specific ruling).

You do normal damage and 1 is a crit.

Thank you very much guys!