It turns out the cop was actually only pretending to be a cop posing as an undercover cop.
“I know what I’ll do. I’ll tell her I’m an…undercover officer. And that she should meet me at the…police station. She’ll never suspect a thing.” From the mind of the least imaginative cop in history came a plan that was so crazy it accidentally worked. Either this Portland-based prostitute just couldn't believe that a real cop would make up such an obvious story, or she simply didn't realize that this is the state of law enforcement in Oregon. For future reference, walking into a police station to meet your John is pretty much a guaranteed way to end up at the police station.