There’s evidence to suggest that Kristen Nelson’s Chief Vick knew from the very beginning that Shawn Spencer was pretending to be a psychic.
On USA’s Psych, Kristen Nelson’s Chief Vick may have always known that Shawn (James Roday Rodriguez) wasn’t a psychic. For most of the series, Gus (Dulé Hill) and Henry (Corbin Bernsen) were the only main characters who knew the truth about Shawn’s gift. Lassiter (Timothy Omundson) always suspected but could never prove it, and Juliet (Maggie Lawson) didn’t discover Shaun’s secret until season 7.
In the Psych series premiere, Shawn’s perceptiveness ultimately made him a suspect in a crime, as his heightened awareness of his surroundings allowed him to know things that he couldn’t properly explain. To cast suspicion off of himself and to get the police to take him seriously, Shawn pretended to be a psychic who receives “visions”. After solving the crime, Shawn had no choice but to keep the lie going, due to a conversation that he had with Chief Vick, who gave him a firm warning that if she ever found out that he was lying about being a psychic, she’d prosecute him for hindering a criminal investigation. After that, Shawn used his “visions” to solve crimes for the Santa Barbara Police Department for eight seasons.
Despite Chief Vick’s threat, it’s possible that she, like Lassiter, never fell for Shawn’s ruse. Whenever she was told about one of Shawn’s visions, she could have just been playing along. It’s important to note that Vick was shown to be an incredibly intelligent character, and there were plenty of times when she could have come to the conclusion that Shawn was faking it, especially since many of his “psychic episodes” were less than convincing. There’s evidence to suggest that this may have been the case. In one episode, she noticed that Shawn was secretly getting help on his cases from Henry, which he shouldn’t have needed if he was really a psychic. When Shawn had to take a lie detector test, Vick appeared visibly worried about what he might say, and smirked when Shawn found a way to beat it. Shortly before Harry Trout (Anthony Michael Hall) took over her job, Vick admitted that to solve cases, she allowed certain things to slip by.
It could be that she said those threatening words to Shawn in the Psych pilot because she knew that if she ever had evidence of wrongdoing on Shawn’s part, she’d be obligated by the law to take action against him. If Vick understood that Shawn was simply good at being a detective, she may have decided to look past his antics. After all, what was important was that he got results.
If this is what Vick’s mindset was in regards to Shawn’s lie was in Psych, it’s not far from Lassiter’s approach, particularly in the later seasons. He seemed to have the same idea about Shawn in the Psych series finale. When Shawn made a goodbye video for everyone, Lassiter stopped watching when he realized that Shawn was going to confess that he wasn’t a psychic. Because of plausible deniability, Lassiter knew it was better not to have proof. This may have been the opinion of both Lassiter and Vick.