I agree that it's not the best idea to feed live because of the biting issue, but if a snake isn't eating, sometimes they are more attracted to a live mouse that smells like a mouse and wiggles. It gets them eating. The mouse in that situation is also not allowed to run around the cage, creating more of a hazard for the snake. On the flip side, what happens to wild snakes? They don't have the luxury of finding thawed prey that they can just swallow. Has anyone ever caught a snake that has bite marks on it? Snakes are supposed to kill their pray.
I recomend feeding frozen if people buy a snake, but if done responsibly, I don't pannic if someone feeds live...especially if that's what they're snake is eating.