they usually do 20% especially if none are left in-stock.
the phone rep just needs to get approval if there's substantial evidence (doesn't always have to be pics). then again, having holes in the box, missing elements, or major box surface sticker tears (from labels) would help you get the larger discount. if the box was crushed, that would also help w/ the getting 20% discount.
if amazon is anything like target.com, customer support reps also look at purchase history to make a stronger case for larger discount approvals. from what i've been told, support mgrs (who grant approvals) usually say, "it's only a box. are the items inside still complete and undamage?. of yes, 10% off at the most to avoid more postage cost and time wasted".
unfort, creases are normal when mailing larger sets like this so 10% off would be considered by some as a "gift". I learned to accept creases even as painful as it was.
heck, i just canceled a bricklink order consisting of 1 BP and 1 QAR because the buyer insisted on "mint" boxes arriving to him in Singapore. ha