Cops frequently go around to peoples listed addresses to serve warrants, and frequently waste their time doing so because the people know they have warrants and are hiding out from the cops. I'm not even sure having an address for someone with a warrant gives probable cause to search their residence if their girlfriend, dad, best friend or casual acquaintance says, "No, officer, I haven't seen him in weeks, sorry. " Showing up for their free tickets is just an admission they are a person wanted for criminal non-payment of child support, so I don't see the problem. They were already wanted for a crime, the sting just induced them to come to the police station where they were arrested for that previous crime. It's morally dubious as a deliberate faleshood, but it's not exactly a miscarriage of justice. Cops do this all the time (hence the reference in the Simpsons episode years ago) and I doubt they'd continue doing so if it jeopardized cases, but I can't see why it would or should.