Stress Signs - Refusing Food

Some dogs just aren't very food motivated (this is usually shocking to owners of highly food motivated dogs because it is such a big change.) But sometimes dogs, even food motivated dogs, don't want to eat because they are too stressed. Different dogs have a different threshold for how badly nerves affect their ability to eat. Max stops eating about as soon as he starts being nervous. Hero on the other hand would almost never get too nervous to eat.
Sometimes using higher value treats can help. This particularly helpful for dogs who are also calmed by eating. Don't worry, you won't spoil your dog by giving him extra yummy treats when they are nervous, if anything it will help with desensitizing them to the stressor.  

A particularly dangerous thing to watch for is dogs who quit drinking water when they are stressed. Not drinking for a little while is probably okay, but dehydration can be dangerous and just adds to the overall stress level.