Size Matters - S4-E5
Continuity mistake: Shortly after Phoebe frees the blonde girl from the clay, she tells her to run "before Gammill sees [them]." But Phoebe hadn't learned the demon's name at any point. Leo and Piper do find out his name, but not until later. (00:20:00)
Suggested correction: Gamill and Finn are talking when Phoebe is at the house. It may be possible that Gamill's name was mentioned by Finn in conversation.
Size Matters - S4-E5
Continuity mistake: Piper suggests that Paige orb in place, because the clay is still wet enough that it will collapse if she's not there to support it. But when Paige actually does orb, the clay cracks and collapses into powder as if it had been bone dry.
Size Matters - S4-E5
Other mistake: Since when are managers, on a trial basis no less, allowed to renovate and change the name of a club?
Suggested correction: Piper says in the episode that she allowed him creative control because the club wasn't doing well, and he was well-known to be good at what he does. It's made clear throughout the episode, by way of him telling her multiple times that if she doesn't like it that he'll get rid of it, that she still has full veto power on any changes.