I'd heard about people getting hired to test the faithfulness of their partner -- hire some guy to randomly meet up with your girlfriend somewhere you know she's going to be, having him approach her, see if she takes the bait (or vice versa, if you're the girl testing your boyfriend's loyalty). I think there's a company that does this in the UK, maybe there's more.
But this I hadn't really heard of before - at least not outside far-fetched courtroom dramas - people getting hired to seduce half of a couple and bring pictures to the other half for divorce court.
It's interesting for more than a 'stare at the train crash' kind of way. Look at how they plan these seductions -- it's not some guy running into her at a bar. That's probably too hit or miss for guys who don't have pick up artist training, so they're smart. They set up the social context. Note the presence of other women, including at least one female friend. Note the peer approval for her actions. Note the way it "just happened" that the party continued in the hotel. Note how other people just drifted away so it "just happened" to be her and him in the hotel room at the end. Note also, alcohol :)
* Use your turf, not hers
* Make logistical moves (bar to hotel, hotel party to hotel alone, etc.) seamless
* Groups are great if your friends know what they are doing
* Context matters. A lot.
(Another curious thing just hit me -- with that UK company I remember that 'tests' for loyalty, I remember reading that one of their rules was that they don't send testers/seducers who are significantly better looking than the person they are trying to test. That seems weird to me. Most guys who are worried about their wives or girlfriends cheating aren't really worried about the average guy on the corner - they're worried about how she'll react when given a chance with smooth-looking eye candy. And same for women. Odd.)