To be honest, I usually will accept if within 10% overcook or rare because re-cook the same beef will cause bad taste or overcook usually!
However, if the waiter answer my complain in this way, I will 100% sure to answer him : Can I pay the bill with a less discount liek 20% or 40% off? $100 and $80 also 爭少少啫, 你相就下, 做人唔使拾得咁正架 ! And see what can he say! Hahahaa!