re: Costa Rica Rental Car

If you have a credit card that provides coverage, you can decline the extra insurance. The rental folks are going to push back, but can be done. Prior to leaving, contact your credit card and have them send you proof of rental coverage, with your name and last 4 of your acct number listed. Make sure this card is used to pay for the reservation, and any other fees associated with the rental.
Rented cars in CR maybe 5 times, as well as about 5 times in MX over the past 4 years. Sometimes they will put a ridiculously high charge on the card and refund when you return - like $20K. Make sure you have room on the card.

The cost of the insurance often exceeds the rental charge, let your CC company battle out the issues should they arise.