Continuity mistake: When Shawn gets in Gus' car by the Psych office, the seat belt he puts on keeps changing position with each shot.
Other mistake: When Spencer is on the phone to O'Hara, his iPhone shows the standby screen, not the screen that comes up when you're talking to someone on the phone.
The Head, the Tail, the Whole Damn Episode - S4-E15
Visible crew/equipment: The scene where Gus is smelling for the first shark and Shawn is 'divining' it. As they round the corner at the dock, a camera and some randoms are visible down the alley for a few seconds. (00:19:00 - 00:23:50)
Ferry Tale - S5-E7
Plot hole: The cops storm the ferry and recapture the 4 prisoners, only to quickly discover that two convicts swapped places with passengers and escaped on a medical boat. This boat powers off and we're later told "by the time we caught up with the boat they'd made their escape", but there's just no way that's possible. They had barely a minute's head start, in wide open water, with multiple high speed police boats in range/sight of them the whole time.
Ferry Tale - S5-E7
Continuity mistake: When Young Shawn tapes his and Gus' legs together he puts the tape on the ground. When they start to run it has disappeared.
Continuity mistake: In the scene where Shawn is brought into his childhood bedroom to investigate Allison's abduction, there is a "Peeping Tom" band poster visible behind him for a few seconds. This was Shawn's bedroom in the 90's, and "Peeping Tom" didn't exist until 2006.
Other mistake: After they trace the number from the vampire bar they bring Marla's roommate in for questioning. Calling a bar, that has zero connection to the murder, and asking for blood wouldn't make someone a suspect or be enough to bring them in for questioning.
The Amazing Psych-Man & Tap Man, Issue No. 2 - S6-E4
Plot hole: The flashback involves Young Shawn and Gus getting ready to go to a comic book convention, Shawn in costume, with his father's consent. This contradicts the flashback in "Shawn Vs The Red Phantom," where Henry won't allow Young Shawn to even read comic books or play superhero with a towel around his neck.
The Amazing Psych-Man & Tap Man, Issue No. 2 - S6-E4
Other mistake: Before the first break when the scene morphs into a comic of the scene that just happened, Lassiter asks "You see him too, Guster?" in the comic on too is misspelled as "to".
Character mistake: When Shawn looks at Curtis Stanzen's file in Leo Quinn's office, guilty is misspelled. It says "gulity". (01:30:00)
Shawn and Gus Truck Things Up - S8-E7
Continuity mistake: Gus walks over to Shawn with toys in his hand. The shot changes, one of the toys disappears. (00:25:16)
Shawn and Gus Truck Things Up - S8-E7
Continuity mistake: Shawn throws an oven mitt at Gus. It bounces off him and lands on the floor. When Gus gets up, the oven mitt is gone. (00:38:37)
Chosen answer: "Psych: The Musical" was supposed to air during the regular season 7 schedule, before Chief Vick is suspended and Jules discovers Shawn's lie, but the network decided to push it back to air as a special episode, sort of as a tie in with the holiday season and a lead in to season 8, which was to begin only a couple of months later.