The Facebook pages that's popped up on my feed is called something like the Innocence Keepers. I don't know if they all do this but they use 'decoys', being young children to speak to them, they obviously make their age known pretty quickly and see if the beasts want to carry on. I don't know how they know these young people, whether they're family/close friend or whatever, but they told the paedo from Leven that one of the decoys was quite shaken and disturbed by what they had to read/see, which I find extremely uncomfortable as the kids are obviously being exposed to some pretty grotesque language, suggestions and images.
Fair enough if you get some 25 year-old to pretend to be a 13 year-old girl and try and catch them out*, but if they're actually having children look at this stuff, it's not a nice thought at all.
Another thing is the whole cringe-factor of it, you'll hear the paedo hunters trying to sound official and formal. One of them tried to give a disclaimer during a video saying something like, "please refrain from approaching the property or the residents inhabiting such properties", then the camera moves down to show the boy in paint-splattered trackies and Dunlop slip-on trainers.
*although they wouldn't technically be doing anything illegal here, if anything the paedo hunters would be for fraud.