Visible crew/equipment: At the start of the final courtroom scene, when the first shot is on Cole with Morris behind him, the boom mic is visible over Cole at the top of the screen. (00:34:25)
We All Scream for Ice Cream - S3-E10
Visible crew/equipment: When Prue and Phoebe are trying to pull the girl out of the ice-cream truck, in one brief shot, you can see the wires holding the girl up.
All Hell Breaks Loose - S3-E22
Visible crew/equipment: During the scene in the kitchen, after Piper reads through all the faxed interview requests, in the wideshots facing Darryl the reflection of the moving boom mic is visible on the glass at the top, center of the screen. (00:21:15)
The Demon Who Came In from the Cold - S3-E19
Visible crew/equipment: After Prue removes the piece of Belthazor flesh from the freezer it cuts to Cole finding Phoebe's note in his pocket with a closeup of Cole, and at the start of the next shot the reflection of the boom operator holding up the boom pole and mic can be seen on the glass window, behind Pirelli/Vornac. (00:28:05)
Visible crew/equipment: After Lukas kills the other demon so he can move forward with his plan to go after the witches, when it cuts to the manor's foyer as Prue and Phoebe walk in, the green T-mark is visible on the rug at the bottom of the screen. (00:08:15)
Visible crew/equipment: After the Grimlocks enter the manor Leo calls for Piper then rushes out of the kitchen, and when it cuts to the shot of the dining room the edge of the crew's black mat is visible at the bottom of the screen. The black mat is again when the sisters are pulled into the time portal, though the only thing we should be seeing is the fringed area rug. (00:04:00)
Blinded by the Whitelighter - S3-E11
Visible crew/equipment: After the opening credits, when it cuts to Piper and Leo in the dining room the green tape mark is visible under the table, and the red T-mark and long blue tape mark are also visible on the crew's black floor mat behind Leo. (00:04:45)
We All Scream for Ice Cream - S3-E10
Visible crew/equipment: When Phoebe gets an IM on the laptop Prue walks over to her, and just as Prue sits down at the table we can see the blue tape mark on the floor, where she had been standing. (00:05:50)
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)
Visible crew/equipment: After Phoebe tells the others that Emilio will be getting arraigned at night court in an hour, when it cuts to Leo and the sisters walking in the court hall, the shadow of the boom mic is moving at the top, left side of the screen. (00:33:45)
Magic Hour - S3-E2
Visible crew/equipment: When Prue and Phoebe see Piper arrive home, a boom mic dips into the shot. (00:01:30)
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.