Since he was buying their insurance, he said there would be no additional liability. But when I checked, if he happened to have a wreck while drinking or under the influence, I would be fully liable. Also, I believe that even with full insurance coverage by the rental car company, there are limits, so that a person injured could sue me for more than the insurance policy would cover. Am I thinking correctly in not doing this fellow a favor by renting the car for him using my credit card?