This was posted on FB by a local (to me) vet behaviorist :
Reisner Vet Behavior
Tuesday's Pearl: Food is not an effective counter-conditioning tool when it’s being offered by the scary stranger.
If you’ve ever raised a puppy, you probably asked all kinds of people to offer her food and interact (safely) with her. This is a good strategy for socializing puppies who seem reasonably confident around unfamiliar people. But...with worried or fearful dogs of any age, it’s often not a great strategy for a few reasons:
First, fearful dogs are, well, fearful – any interaction with an unknown person can simply be threatening to them. Forced "greetings" can make them more fearful, not less.
Second, when offering food, people usually stare, bend and reach towards the dog – which, in dog language, can be loosely translated as "I'm going to eat you now."
Third, significantly fearful dogs may defensively bite even after taking and eating the food. The treat itself is basically uncoupled from the person offering it. This is common, and can be explained by understanding that the dog is ambivalent (“This person is creepy, but that liver is irresistible!”). He may choose to take the food as the arm reaches out, and at the same time be intimidated by that arm. But as it’s withdrawn after the treat is taken, the arm is a little less intimidating, while your dog is just as ambivalent. Th upshot is that fearful dogs commonly bite body parts that are moving away from them.
If your dog is worried around unfamiliar people on leash walks or in your home, ask them to ignore him (you might need to define "ignore" and tell them to resist eye contact, reaching, bending, petting and feeding. Instead, *you* should be the one to make it rain liver in the presence of strangers. This simple strategy counter-conditions the fear by associating the scary clowns with food and simply avoiding intimidating postures and interactions altogether. If anything is going to help your dog feel less frightened when strangers are looming over her, it will be a consistent sense of safety and predictability.
Reisner Vet Behavior