(my usual disclaimer: sorry if this is covered elsewhere, I couldn't find it in a search).
I'm using a Free Rental Day Certificate from Avis.
I always use Diner's Club for my car rental so I never need worry about supplemental insurance coverage. The "Free" rental day still costs me tax (about $20).
My question: Will they run my Diner's Club before my rental to cover the tax, and if so, will that cover me insurance wise?
If I have to get supplemental coverage, that rather negates the value of these free day coupons that Avis is now sending me after 15 rentals.