Most cabs on the LV Strip do not accept credit cards. Possibly because of the number of people who over extend in the casinos? Who knows! It was a surprise to me when I first arrive at McCarren but proved to be true for the rest of my trip as well. So always bring cash OR request a credit card cab (which any hotel or airport attendee will do for you if requested).
My beef is that some of the drivers, knowing that you're a tourist, will purposefully take you on the highway to avoid the "traffic" on the Strip. I am a tourist, so what the heck do I know? Result: paying $28 to get from one end to the other for dinner, and only $13 on the way back.