Visible crew/equipment: When Piper is taken by Wong's men Mark shouts for help, and just as Prue tells Phoebe to call 911 from the car, the blue tape mark is visible on the rug beside the table, where the sisters had been standing before rushing out. (00:36:05)
Visible crew/equipment: When Prue is flicking through TV channels, just as Phoebe walks into the bedroom and stands beside her sister, we can see the movement of the camera operator and camera in the reflection within the standing mirror, near the door. (00:34:05)
Visible crew/equipment: After Piper takes the picture of Tony Wong holding the newspaper, when she and Mark quickly drive off, we can see the actors' large yellow T-mark taped to the ground near Wong and his men. (00:28:35)
Visible crew/equipment: When Aviva tells Phoebe that she wants to go upstairs because she's not feeling well, Aviva walks into the bedroom and just as she grabs her backpack part of the T-mark is visible on the floor where she stands. (00:33:45)
Wicca Envy - S1-E10
Visible crew/equipment: After Jaime tells Prue that she's the hardest working woman he's ever met and believes she's innocent, Prue walks into the office to access Hannah's computer, and just as Prue sits down and moves closer to the desk, the blue T-mark is visible on the floor, under the office chair. (00:24:30)
From Fear to Eternity - S1-E13
Visible crew/equipment: When Andy walks into the manor to speak with Prue, just as she tells him it must be bad news, we see the reflection of the boom mic on the glass door. (00:09:45)
The Wendigo - S1-E12
Continuity mistake: When Andy is lying on the ground unconscious The Wendigo rips open his shirt popping all the buttons, but in the closeup of Andy's face his shirt is still buttoned up. (00:38:50)
The Wendigo - S1-E12
Visible crew/equipment: When Phoebe joins her sisters in the kitchen before her first day at work, the reflection of the moving boom mic is visible on the glass cabinet, at the top of the screen. (00:10:05)
Which Prue Is It, Anyway? - S1-E16
Continuity mistake: While Phoebe explains the slam man training system Piper puts on Phoebe's boxing gloves, and when Prue says that demons don't play fair Piper playfully raises her left arm to Prue's forehead, but in the next shot facing Prue it's Piper's right arm that's raised. (00:04:00)
Continuity mistake: While Andy and Darryl are at the station talking about why Andy's been "walking around...like a zombie," Andy places a pencil behind his ear, but when it cuts to Inspector Blakely walking in behind Andy the pencil has vanished between shots, but it reappears again in the next shot. Then when Andy borrows the photograph of the knife, once again the pencil vanishes between the closeup and wideshot. (00:09:10)
Plot hole: When the Avatars agree to rewind time they say that they can either put the world right or save Brody but not both. This doesn't make sense since they're rewinding to right when they put everyone to sleep, which is before Brody was killed.
Other mistake: When Phoebe gets the premonition to see all the loss, she sees the scene where Piper dies in All Hell Breaks Loose. Since time was rewound this event never happened in this timeline, and we're never given any reason to believe Phoebe would know this happened after the time reversal.
Other mistake: After they talk to the Angel of Destiny for the first time, they send Leo to ask the Elders if he is legit. After Leo leaves they find out about Agent Jackman, and the following events unfold. After Jackman busts them Piper calls for Leo and tells him "It's OK, you can orb" and he appears asking her "What about Agent Jackman?" Except that Leo was gone before they found out about him and the girls hadn't told Leo yet that he even existed. (00:09:09 - 00:21:58)
Other mistake: When Phoebe is trying to summon Angela the spell doesn't work and Leo says that she needs the power of three. We've seen this spell done with just one sister in the past and it's never explained why they'd need to do it together this time.
Continuity mistake: The furniture used throughout the show regularly gets blown up or destroyed but then mysteriously re appears later on or in the next episode.
A Wrong Day's Journey Into Right - S6-E20
Revealing mistake: Right after Paige is orbing out, the camera is on Phoebe and on her right, you still see Paige's shoulder. And then it cuts to Paige orbing back in.
Factual error: During the ritual, we can see that the snake that is magically transformed into a man is a milk snake. But it's not poisonous, it's a colubrid. The creators apparently wanted to use its resemblance to a poisonous coral snake, which is an elapid. (00:02:35)
Continuity mistake: When Paige is at the bar with her newest charge we see the same extra walk by 3 times, going the same direction each time.
I've Got You Under My Skin - S1-E2
Revealing mistake: At the end of the episode when Phoebe and the other two are at the bar you can notice that Prue straw in her drink goes in and out of her drink a great deal.
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.