When I used Thrifty, which is Dollar also, I was given an additional discount for the membership. I would join and recheck your rates. Keep rechecking because mine were going down until three weeks out. I think I was emailed my membership number as soon as I joined, or I called and they gave me it to me. Bu, that was their other company Thrifty.
If I wasn't happy with the car sitting waiting for me all I had to do was let the attendant know, but never had an issue.