Recent fine print from Enterprise

Read the fine print on your rental contract, then call the card. The devil is in the details. Two charges to worry about, that can double the repair costs of a crash are "loss of use" and "diminishment of value". For the first, the rental company expects you to keep paying your daily rate while the car is repaired. A car involved in a crash is worth less; the second estimates this loss.

Before taking sides instinctively, knowing that lawyers are out to get you, ask yourself what would be a fair understanding if you lent your car to a friend with substantial means? Both of these charges are entirely reasonable, and you're agreeing to them when you sign the rental contract. If you don't like these terms, walk.

Oh, but that it be so simple to get a credit card company to understand that you've signed such an agreement, and to stop mis-advertising their protection.

The rub comes when credit card companies try to avoid paying these charges. For example, they ask the rental agency to prove actual loss of business because the car was unavailable, even though the fine print explicitly states that the rental agency need not prove this. Aside from the money, the rental agency has legitimate privacy issues concerning disclosing this business data.

I don't have this card, primarily because I prefer the online transaction details available from American Express, together with their greater propensity to side with consumers in disputes. However, it is hard getting a straight answer, in part because some rental agencies have understandings with some credit card companies to not apply these charges, in return for expedited handling of the rest of claims. This could be the case for you, and yet you'll never know for sure, even if you ask a dozen people.

The "primary" coverage is indeed worthwhile; with "secondary" coverage an accident is a three-way cluster fog of ridiculous paperwork involving your personal auto insurance. I find it worth the per-rental fee to make Amex primary, just to avoid this cluster fog ever again. I did save these fees in the end, which will pay a decade of these per-rental fees for my rental frequency. (I hit a deer in upstate New York. Don't.)

If you have personal car insurance, then check with them but you should be fine for liability. If you don't, most liability coverage is inadequate to protect the typical wealth of someone who can afford to rent a car; it merely meets the legal requirement. There are upper middle class people in New York City who don't have personal auto coverage and rely on e.g. Zipcar, not realizing how a single incident could endanger their retirement savings.