I recently rented a car in Charleston, WV on a Sunday night for a 5 day period. I gave the agent a "free day" coupon that had a minimum 3 day rental period agreement. When I got to work on Monday morning, my boss told me that he a car for me and to return the rental to the airport on the way home.
Long story short, Avis charged me just $3.05 for the gas usage(12 miles)with no questions asked. Now if they would just partner with US Airways for extra miles.