And your server will have no problem spitting in or otherwise doctoring your food. No problem at all.
Solution: Stay at home. Food is better anyway.
No, they aren’t gonna know about it beforehand. Their chance for spitting is when they still think they might get a tip -— unless they just spit in everyone’s food, and if they do that they’ll eventually be caught and charged with attempted assault (legally, intentional bodily fluid inclusion is a serious crime).