@carpoolingma, It’s the process of making the kid and the family trust of the predator. It may take a while and it rarely involves anything sexual at the beginning. In some cases, it’s been taking the kids to “special” events, such as bowl games, so that the kid feels comfortable with the adult and being alone with them. There’s a documentary out there about the Penn State case, and it explains it and shows it pretty clearly.
But as the OP’s question, I think it’s a continuation of what you taught them when they were little. If they are feeling uncomfortable with a situation, they should leave. Any touching that they are uncomfortable with is inappropriate. And you want to be sure that they’ll be comfortable talking to you if they feel there’s a situation that doesn’t feel right.
At the same time, I wouldn’t want fear to make my child uncomfortable expressing affection with a hug, for example, so I’d really keep the emphasis on touching that felt inappropriate and/or sexual.