Correct me if I am wrong, but most north americans are covered for SLI by credit card or other insurance, so this issue does not often arise for the local market.
If you are not local, however, it's a different story.
Originally Posted by
AutoSlash
Just to be clear, the car rental company is required to maintain the minimum liability insurance required by law in the state you are renting in (except for California where there is no requirement). Liability has nothing to do with the rental car you are driving. All coverage relating to damage to or theft of the rental car is covered by CDW/TPW.
SLI on the other hand extends liability coverage for you to $1M for any damage you may do to someone else's property, for example, an at-fault accident where you damage someone else's car, injure someone or damage property like crashing through a storefront window.