Continuity mistake: In the scene where Eva is teaching the sisters about ways to draw power on All Hallows Eve, she cuts an apple in half and puts a leaf over the seeds in the center. The leaf goes from small and only covering the center to bigger and covering more of the apple.
Sight Unseen - S3-E5
Factual error: When developing a photo it's first put into a developer chemical, which shows the picture up, then a stop, which stops it from developing anymore, then a fix which "sets" the photo. But in the basement, Prue puts the exposed photo into a tray with chemicals in it where it starts to develop, then into a second tray where it develops fully.
Sight Unseen - S3-E5
Continuity mistake: Cole goes to the manor, turns the AC on, knocks a lamp on the ground and opens a window, then shimmers up to the attic. When the sisters come home all the windows are open, but Cole opened only one downstairs.
Sight Unseen - S3-E5
Factual error: In the scene where the invisible demon is entering Cole's office, the courthouse shown before the elevator is a New York City courthouse, not San Fransisco. It's confirmed by the presence of a NYC Taxi.
Revealing mistake: When Prue is practising using her powers while astral projecting, when Phoebe walks away to go see her in the attack you can see the makeup they used in an attempt to hide her tattoo on the right side of her back. It looks as though she's been bruised there. (00:00:43)
Visible crew/equipment: After following the signs that lead to the demolition site, when Prue unlocks the chain on the door and enters the loft, the T-mark is visible on the floor at her feet. (00:03:45)
Continuity mistake: When Prue was talking with the shut-in and the security guard comes up and knocks on the door you can see the the chain is on the door. When he knocks again and says he is coming in and tries to open the door the chain is off.
Audio problem: When Prue is at the dentist, she grabs a guy and he says, "What, what did I do?" to his girlfriend, but his lips do not move.
Revealing mistake: At the end when Prue is fighting the demon you can tell she is holding on to her safety harness when she is in the air kicking him.
Continuity mistake: When Prue is in the basement with the priest she has curly hair, but when she comes upstairs to vanquish Vinceres it is completely straight, but she definitely didn't have time to straighten it.
Power Outage - S3-E7
Continuity mistake: When Cole drops Phoebe off at the manor after their date, Phoebe lowers her hand from Cole's face when they kiss, but then it's suddenly back up near his chin. (00:22:20)
Power Outage - S3-E7
Revealing mistake: When Astral Prue kicks Leo/Balthazar in the face during the training drill near the start of the episode, her foot misses his face yet he still reacts as if hit.
Power Outage - S3-E7
Revealing mistake: Alyssa's tattoo is visible when Phoebe leaves Cole's apartment after she fought with her sisters.
Power Outage - S3-E7
Continuity mistake: During the training drill, Piper fumbles for a knife on a table in front of her. In the shot of the table, she loses hold of the knife as she pulls her hand up, but when we cut to a long shot, it is back in her hand.
Sleuthing With the Enemy - S3-E8
Revealing mistake: When Cole / Belthazar grabs Phoebe to use her as a hostage, you can see, very obviously, that he doesn't pull her. Phoebe actually steps in front of him willingly, despite the look of fear on her face.
Sleuthing With the Enemy - S3-E8
Revealing mistake: When Phoebe throws the potion at Cole's coat, the vial doesn't shatter, even though it sounds like it. Watch closely, and you'll see the purple, unbroken vial bounce off the coat and away out of shot without any of the potion touching the coat.
Sleuthing With the Enemy - S3-E8
Other mistake: When Piper puts the Belthazor flesh into the Belthazor vanquishing potion, she is the only one that gets "blasted" back even though she is the one standing farthest away from the stove and the potion.
Sleuthing With the Enemy - S3-E8
Other mistake: Cole is supposed to be one of the most powerful demons alive, but a small cut from Piper weakens him to the point where he can't even shimmer or keep up his "Cole" appearance.
Sleuthing With the Enemy - S3-E8
Audio problem: When Phoebe fights with Krell in the mausoleum, the vial containing the Belthazor vanquishing potion is heard smashing, but after Krell is vanquished, Phoebe picks up an unsmashed vial and uses it to stage Cole's escape.
Answer: That was a mistake in the series.
Also, the episode is called 'Babies First Demon' and this alone tells us that it's Wyatt's first time in the field (so to speak) and as the sisters say, they've done a good job of clearing up their own magical messes so far. Nobody really knows how advanced Wyatt's powers are, or will become. That's why the cleaners appear, to nip things in the bud. The Cleaners didn't want to chance that the sisters could clean Wyatt's magic up, just incase they couldn't. Therefore intervening themselves, just in case.