A few tips for getting a stubborn snake to eat...
1) Make sure the snake is warm enough. If the snake is in a cool area it's metabolism will be significantly lower.
2) Make sure the food is warm. A living mouse will obviously have a higher temperature than a dead room temperature mouse. If you soak the mice in warm water before using them the snake may think they are alive and be more interested.
3) If a ball python is rejecting mice or rats try gerbils.
4) Don't be afraid to rub the snake with the food in order to get it's attention.
5) Make sure you are not feeding your snakes too often. if the snake doesn't eat today wait a few days and try again. It may still be digesting its last meal.
6) If the snake is new let it get acclimated to it's new environment before trying to feed it. Also ask if it had been fed just before you purchased it.
7) Some snakes may be more accepting of live food. Live food is nothing to be afraid, just don't leave the animal with the snake if it doesn't accept it.
8) If your snake grabs the food off the tongs and then drops it you can try holding on to the prey item and lightly tugging and wiggling it. This will make the snake thing it is alive and he will hold it tighter to try to kill it (gives him satisfaction). Tugging on it for 10 seconds is enough.