It seems that if you get too cheap a rate with some car rental companies, they try to make up for it with an additional charge for additional drivers, something like 5 Bucks a day or so.

In the case of my wife and I, what are the implications of not registering a driver, if the rental company even finds out? I asked my insurance company, figuring this might be a problem, but they said any contract violations were beteween me and the rental company, and as long as the authorized driver gave permission, we were both covered.

I'm assuming if I bought any insurance from the rental car company might be invalid, and maybe the secondary coverage provided by the credit card might be invalid as well. As I never buy the waivers in the US, and I can eat the deductible, especially for $5/day, I don't see any downside. Their contracts make it sound like a major felony to let an unauthorized driver drive, but then their rental agents make you sound like an extreme risk taker if you don't buy their coverage for damage, accident, liability, etc.

Or, am I missing something here?