I do see the option, it asks me to leave the feedback
pos neutral or negative...
I do not leave feedback until they do so first though...I'm bend over backwards to satisfy them, and I'm still at 100%. From exception shipping skills to complete wimpiness on customer service ( to a point ) ....but I think that not leaving feedback until the end seems to be an added incentive?
It might be true that this guy did not like your shipping, thought you owed him a discount due to that...sometimes paying the cost of shipping it back doesn't make financial sense...
He could have also sent you an email implying that he'd leave negative feedback...
'I'm just not happy with this transaction. I feel you failed to ship properly and I don't want to be out the shipping costs back'