Permissible Deception: "You Have a Tax Refund...."

AP via Maryland Daily Record, October 23, 2007:

Forty people promised a tax refund of more than $500 were arrested on criminal warrants when they appeared at a state office building to collect the refund, authorities said.

The Anne Arundel County Sheriff's Office sent letters to 500 people with outstanding warrants in October, saying that a computer error meant there was a $572.26 check for them that could be picked up in person.

...

The 500 represented the most recent criminal warrants, ranging from misdemeanors to felonies. The letters were sent Oct. 5, telling the subjects that a computer error had been detected in the "tax break indicators" used to determine their tax rates.

Law enforcement is permitted to engage in a substantial amount of so-called "permissible deception" in order to get open warrants served as well as to obtain confessions. I have not read the case law on such deception, but have heard of prior stunts such as a fake casting call for Robert DeNiro-film acting extras in New York. I do not recall clearly the boundary of permissible versus impermissible deception.