They should be the judge of this. Personally, I have always fed live. I know that there are dangers of doing this. That is why the snakes are never left alone with a live prey just sitting in their enclosures. I hold it for them by the tail. If they seem disinterested, then the prey goes back into it's own tub until the snakes are hungry.
If a person feels uncomfortable feeding live, you can always switch over to FT. Here's something I found on switching:
http://www.herpcenter.com/feeding-sn...en-thawed.html