Auto Insurance Claims: Claim Coverage for repairs, worst case scenerio, claim coverage

Question
My wife was involved with a rear end collison last week. The other individual was admittadly at fault. We had our vehical inspected for repairs by 2 different shops who both quoted very similar amounts to fix the damages. After showing the car to the insurance adjuster, they provided a quote and check for the repairs at roughly $500 below the other quotes. We have not signed anything and have done nothing with the check.
Furthermore, both repair shops informed us that the repairs will take 1 weeks time after parts are in; the insurance company gave us a voucher for only 3 days. We need the rental to go to work in on a daily basis.
We have never had an auto accendent before and are fearful that we will be left with the difference between the final repair and the settlement amount.
Where do we go from here ?

Answer
Did the adjuster explain the supplement process to you?  Once you drop off your vehicle and it is torn down, the shop is free to request a supplement from the insurance company for any justifiable parts or labor that are needed.  

Shops always write their estimates in the worst case scenerio which also means the highest possible profit and insuranace companies write the best case scenerio which means not wasting money on unecessary parts or labor.  Through the supplement process they will meet in the middle.  As far as rental, the insurance company only owes for reasonable labor based on the needed repair time.  As your vehicle is drivable, there is no reason why the shop cannot have all of the parts present when you drop off the car.  If they can then show a justifiable reason why more time is needed, this is also negotiable.  

Good luck!