Always, I mean Always, make sure that the driver of the rented vehicle was authorized as driver on rental contract.

You hate to ever learn an expensive lesson. I just witnessed first hand from a funder's point of view, a case that had all the makings of a $5 million case but ended up settling for a shade under a million. Funders were just lucky enough to get out with their investment back.
Here's the scenario. Plaintiff was a passenger in vehicle #2. Vehicle #1, a renta- car[under the old rules] hit vehicle #2. Vehicle #1's driver was highly intoxicated and was actually prosecuted. Plaintiff was in a coma for 3 weeks post-accident and suffered pretty significant TBI. Looks like a great case, right?
Well ordinarily under the old rules it would be. Here's the catch. Defendant driver, the girlfriend of the renter ,was not listed as"a driver" under the rental contract and furthermore she allegedly took the car without permission. The attorney never addressed these two issues until it was too late. Accordingly, the case tanked.
Moral of the story; In any renta-car case, establish that the defenndant driver was a listed driver under the rental contract and don't forget permissive use either. Good luck!