Factual error: There is no way Laurel Lance would have been allowed on the prosecution team for Moira Queen's murder trial. Due to the facts that she both dated and as a lawyer represented the defendant's son, the defendant's daughter used to intern for her, and her boyfriend was one of the people killed in the Glades, it would have taken all of two seconds for the court to have her removed if she didn't willingly recuse herself, since her presence would be a major conflict of interest.
Family Time - S1-E9
Factual error: In the barn, one of the kids shoots Cameron, then drops the gun and flees. Cameron picks up the gun and checks how many rounds are in the magazine and then puts the magazine back in. However, after that, she pulls the slide back to chamber a round. But the semi-automatic pistol would already have a round in the chamber since it was just fired, and her action should have ejected an unspent round, which it doesn't.
Factual error: Dario Brando dies in 1880 (date on the gravestone) but when he was screaming at his son from his bed, Dio was reading "The Rise of Silas Lapham", which while being appropriate for his character, would be published only 5 years laters (started serialization in 1884).