Have you ever seen Dateline NBC do their "To Catch a Predator" sting operations? They instigate setups to try and catch people soliciting minors for sex over the Internet. It's riveting television. But, I just thought of something in terms of the legality of the arrests.
These men (they're always men on the show) are chatting with adults, who are only posing as minors. So how can they actually be charged with soliciting a minor for sex over the Internet if that's not really what they did? It's only what they thought they were doing.