The Fresh Prince Project - S1-E1
Revealing mistake: When Will staples his Malcom X poster to the wall, the wall bends back and forth for a second or two.

The Fresh Prince Project - S1-E1
Revealing mistake: When Will screams in front of the mirror, imagining himself turned into Carlton, something went wrong making the composite shot and not only you can actually see the line of separation between the two frames, but the superimposed one exposes a bit of the mirror woodframe before it wiggles into the correct position and covers it up. (00:11:30)
The Fresh Prince Project - S1-E1
Continuity mistake: When Will puts the last of his wall-shaking staples on the Malcolm X poster before the butler's interruption, the poster is almost perfectly flat. When Geoffrey walks to the poster, a bottom corner is noticeably raised. When Carlton walks to it, it's flat again, and raised when Will freaks out at the mirror. (00:07:40 - 00:10:00)
The Fresh Prince Project - S1-E1
Visible crew/equipment: During Will's first introduction to Uncle Phil the camera tilts slightly down to Will and Aunt Vivian on the couch and the boom mic drops into the frame briefly.
Answer: Yes. It's very true. Janet quit at the end of the third season because she claims that Will acted horribly, bullied cast and crew on the set and got her fired for no reason. Alfonso Ribeiro however has called her "cuckoo" and stated that her claims were baseless. He also stated that she was very difficult to work with on set. Even James Avery agreed and often had to remind her that the show was called "The Fresh Prince of Bel-Air" and not "Philip and Vivian of Bel-Air."