Auto rentals have to the absolute worst in that regard. Everything results in the existing contract being destroyed (along with any favorable rates attached to

Auto rentals have to the absolute worst in that regard. Everything results in the existing contract being destroyed (along with any favorable rates attached to it) and needing a new contract created at whatever prices they want. It is a cash grab hoping to catch you when you are at your most vulnerable, there is no technical reason for it. In true western fashion you have to want or need the thing the requires the reservation to be altered, so it’s your own fault the rate has to change. In some states you can’t even use a different credit card without destroying the contract - if you change the number or it gets reissued with a new expiration date then tough cookies to you. I figured out this trick early on so I have a credit card that is only used for car rentals to minimize the chance I’d ever need to replace it. Luckily I’m not flying these days due to Covid and currently live in a state where rental car companies are required by law to accept cash regardless of how the registration was booked, so they tone down the credit card specificity because they prefer you use a card.