In Florida, it is a serious felony crime to travel either within a state or across state lines to meet a minor, or a person believed to be a minor, to engage in unlawful sexual activity. These cases are often the Craigslist cases where an undercover officer will pretend to be a minor on Craigslist or a similar website who is interested in meeting an adult for sex. If a suspect engages that "minor" over the internet, the officer will suggest they meet for sexual activity. When the suspect shows up, he is met by numerous police officers and arrested. At least one of the charges will be traveling to meet a person believed to be a minor for the purpose of illegal sexual activity. This is a very serious felony charge in Florida that normally comes with a significant prison sentence.
These cases can be strong for the state. First, a defendant charged with such a crime is often stigmatized before he gets his day in court. Secondly, as long as the state can prove the defendant is the person with whom the undercover officer was communicating over the internet about the sexual encounter (the fact that the defendant shows up to the meeting at the time discussed online goes a long way towards doing that), it is hard for the defendant to provide a legitimate reason for the meeting. One common defense in these cases is entrapment. Entrapment is also used, but somewhat less common, in drug cases. In these cases, the defendant will say that he initially planned to meet an adult female and thought he was communicating with an adult, but the undercover officer entrapped him by later claiming to be a minor and insisting upon the meeting.
Entrapment is a very difficult defense to make in any criminal case. A police officer being sneaky is not sufficient for entrapment. The defendant must show that the police officer's fraudulent representation created a substantial risk that an otherwise law abiding citizen would commit an offense. A simple offer to engage in illegal activity is not nearly enough. If the undercover officer gave no indications to the suspect about a minor being involved, set up a meeting and then had a minor show up at the meeting, there would be a good defense to that scenario. However, these police officers are trained to communicate in these stings and at some point during the discussion, the officer will make it clear that he/she is a minor (or at least pretending to be), and if the defendant continues with the discussion and the meeting, the entrapment defense is probably not going to work.