I use retailmenot.com for any codes I need for anything. I don't know how good they are for car rental though. Usually if there is a coupon code, they have it posted.
Just be sure to be a real stickler about marking down damage on the vehicle. I have Enterprise trying to scam me right now for 'discovered damage.'
If you have auto insurance, it may already cover you. Check with them and you may be able to save on that.
Not surprising. Let that be a lesson regarding Enterprise. They are known for this. I haven't seen that behavior from anyone else. I typically use Hertz or Avis for work, and Alamo or Budget for leisure.
Dollar is really anal about that. I use National 99% of the time and they are really good about ignoring rock chips and the sort. They tend to cost the same, plus I have Executive membership where I can rent a midsize and then go pick out any car I want (except for specialties such as Jaguar and Hummer).
Another car rental hint - check the price a few times prior to your pick up, especially when it's less than a week. Oftentimes the price goes down significantly. Simply make the new reservation, ensure it is correct and confirmed, then cancel the original reservation. I have made original reservations in the $350 range and eventually got it in the $180 range.