not sure why no one mentioned it: you lose out on Cashback opportunities by using costcotravel.com to book (correct me if wrong, but I know of no Cashback site that recognizes Costco or Costcotravel). There is zero reason to book on costcotravel.com; as pointed out numerously, costco discount codes (if in fact highest, which is not at all always the case) can be entered on car rental Co's webpage...I repeat for the slow comprehending: there is zero reason to EVER book on costcotravel.com

Talking about Cashback websites: when you click thru them to car rental Co's website, you'll later receive Cashback% and also could receive special refer-a-friend of $10-25 depending on particular Cashback site. So using costcotravel.com to book is a very-very losing move WITHOUT ANY EXCEPTION. If Costco and Costcotravel.com desire to become competitive, they better set-up relationships with Cashback sites!!!! Until then, please please please do your pocket a favor and BOYCOTT their site for booking purposes. For research: fine. But no booking on costcotravel.com!!