Buffets (and potluck dinners) are hard for me too. I start with a big glass of ice water with lemon. Then I circle the food and look for the freshest dishes, because some dishes look like they have been out and picked over and aren't attractive.
I take small servings of what looks good, go back to the table and taste everything. If it isn't wonderful, then I set it aside and don't eat it. I have to keep telling myself that it's wasted if I don't need the calories-to counter the I-have-to-eat-my-money's-worth mentality.
I once saw a little round boy at a grocery store salad bar standing at the bar eating from the containers with his grimy little fingers, cottage cheese, potato salad, mac salad. I went and told the store manager and he shrugged his shoulders and said, "What can I do?" I told him, "evict the child and replace the food or at least scrape off the top layer." I went back about 10 minutes later and the boy was still eating.
It completely turned me off from the cold food side of buffets, I always eat the hot stuff. Remeber the sneeze guards only work if the person sneezing is above the guard and not sticking their head underneath to reach the far side of the salad bar.

Also, people don't wash their hands well, then they use the utensils, the utensils fall into the pan with the food, the next person reaches into the pan to grab the utensil....I keep thinking about stuff like that to try to stop myself from eating at a buffet.
Sarah