I had a new experience late last night when picking up my car at DEN. They were sold out, and I got the last car off of the Emerald Aisle (an AWD Subaru). At the check-out gate, the computer was down for several minutes. Due to my patience during the delay, the clerk gave me a half tank of gas and said to return it half full. Completely unsolicited and unexpected, but very appreciated for this business/personal trip. How much flexibility do National's clerks have to give out compensation for problems?