In general, if you drive alone you have assumed responsibility. In most states, if you have not signed an Assumption of Liability a good lawyer or smart insurance company will hold the dealerships insurance company as liable. If your drivers license is not verified, the dealership is at a huge risk for many reasons. Only a lazy and incompetent sales person would risk their job and their companies assets by handing off the keys to an unidentified person. I've encountered people with expired or non-US licenses, illegal for them to drive. People with no or basic insurance, they are not covered to drive alone. I know dealerships where sales persons forget to put demo tags on cars, something very important to have if test driving.
Pretty much whatever you need to rent a car you need to drive alone. The benefit of the sales person being with you is you are fully covered by the dealership. Unless you intentionally wreck the car, or are impaired, you are covered. If I feel someone is impaired or otherwise should not drive a vehicle, I do not offer a drive nor allow them to drive alone.
My posts are solely based on my opinions and for my entertainment, contact a professional if you need real advice.
When you get in debt you become a slave. - Andrew Jackson