Case Law Scenario of Unknowingly Committing Crimes?

No, it is not Susan's responsibility to see if the people in her company were going to Thailand for the purposes of sex tourism. There were no warning signs other than the fact that they were going to Thailand. Lots of people go to Thailand for other kinds of tourism, and believe it or not there is a lot of other legitimate business that goes on there as well. Besides, everybody knows Cambodia is the place to go for that these days.