That's the problem with pet shops- you get a two week period in which to return the animal if it fails to feed, but if you do it right and let him settle in for a week, you only get one or possibly two attempts. So she's already handled him and attempted to feed him (before coming to us for help), then let him settle for four more days, and then had the second failed attempt. Now she has to decide by next Saturday if she wants to exchange him. He's a remarkable snake which makes the decision that much more difficult. I suggested two more attempts, double attempts with the first try in a feeding container, after dark, covered, leave alone for two hours, then retry with a different scenting method in a paper bag in his viv overnight. That gives him four more chances to hit on something he feels like eating. I suggested live, (which aren't available) washed, tuna water scented, chicken juice or fat scented, and since lizards are available, I'd try lizard scenting, actually first. I'd let a thawed, room temp pink sit in a tiny container with a live lizard for several hours. (I just don't have it in me to kill or skin a lizard to get a snake going).
Then she can still decide, on the last day, next Saturday, if she wants to keep trying, with no guarantee, or trade him in.