Many people feel they can not use food rewards with their dog because the dog bites their fingers or is too aggressive with the hand. This is a very common problem many dog owners experience with their puppies.
Eevee the Mal, was developing this problem but in a few short reps shown in this video she learned to take the food properly and her handlers learned to present the food properly to promote correct and safe taking of the food.
Here we see clear use of the "Yes, No, Good," Verbal marker system. Many people try to use more complicated language around behaviors they do not want. Such as Saying "No bite" Or "gentle" when the dog bites the hand. Unfortunately these additional signals can become cues for the very behavior we want to avoid.
If the dog receives reward/gratification when it bites our hand, whether that is the food reward or social/dominance gratification from our reaction, and we teach the dog a word that coincides/predicts this gratification we may actually be teaching the dog to bite us in the same way we teach the dog sit or down. The word we intend to mean don't bite us starts to actually mean "please bite us" since we pay the dog a reward when it happens. We overcome this by non-reinforcing the times the dog bites us with a "no" marker.
We can take this one step further by marking "no" when the dog turns its head to the orientation that would allow them to bit us. Instead we only mark the yes and provide the reinforcement when the dog's nose presses to the palm with the top of the head towards the wrist.