How long have you had him? What are you housing him in (size of enclosure)? How old is he? What was his previous owner feeding him? Live or f/t? If he's a baby, he probably still needs the stimulation of live feedings. How often have you been handling him? Is he settled in his enclosure or does he constantly roam?

It's either a husbandry issue that needs to be fixed, or he's never been presented with f/t before.