Fire Burn, Cauldron Bubble - S5-E13
Factual error: The only instances of "witchcraft" or "witch trials" in America were in Salem, Massachusetts. There were none in Maine or anywhere else. The Salem witch trials spanned 15 months, from February, 1692 to May 1693. Over 200 people were accused of witchcraft, but only 30 were found guilty. Of the 30, 14 women and 5 men were executed by hanging and one man, Giles Corey, was executed by "pressing." Another five died in jail, but none were burned at the stake, which was a punishment unique to Europe.
The Sins of Castle Cove - S5-E17
Visible crew/equipment: When the hairdresser buys a lot of books and leaves in her car, a huge screen and scaffold are reflected on the rear window.
Trevor Hudson's Legacy - S5-E18
Visible crew/equipment: When the woman picks up the hitchhiker the filming equipment is reflected on her car.
Trevor Hudson's Legacy - S5-E18
Revealing mistake: There are 2 scenes involving Jessica inside a car. In the first one the car drives calmly as seen from the outside shots, but from the shots inside the car is speeding. When the episode is about to end the car speeds to the police station and now the exact same projection is played, though this time it makes sense.
Mirror, Mirror, On the Wall (2) - S5-E22
Other mistake: When the sheriff finds the apple, the bitten side has a fresh white colour, instead of the brown colour it should have after the many hours passed.
Mirror, Mirror, On the Wall (2) - S5-E22
Continuity mistake: When Eudora arrives at Jessica's home to apologise, she's wearing a pair of gloves. A shot later, the gloves have vanished.
Revealing mistake: All of the exterior shots of Jessica and Hagarty are wide shots with very obvious stand-ins. Jessica is thinner and younger, while short-haired Hagarty's double is younger, chubbier, and has long hair around the nape.
Dead Letter - S6-E6
Factual error: Unlike the Connie Kowalski character in this episode, real insurance investigators are not trained in arson investigation. Insurance investigators search for evidence of fraud relating to insurance claims. Arson investigators are professional firefighters who have had extensive additional training in arson investigation.
Who Killed J.B. Fletcher? - S7-E14
Factual error: Bremerton, Washington is not a hick town as depicted in this episode (it is the home of Puget Sound Naval Shipyard, a US Navy installation that employs 14,000 people) and the people there do not have southern accents.
Factual error: At the end of the episode after Wayne is shot, there is a brief shot of the outside of the hospital where he has been taken. The sign outside the hospital says Dalesboro, Ohio. Why would someone shot in coastal Maine end up in a hospital in Ohio?
Factual error: "Witches" were burned at the stake in Europe, but not in America. In America, they were hanged.
Tinker, Tailor, Liar, Thief - S8-E15
Revealing mistake: In the second close up shot of Nigel Atkins lying dead, after Jessica drops her Harrod's bag in the chair, it is obvious he is still alive as you can see his pulse on the side of his neck.
Programmed for Murder - S8-E18
Revealing mistake: In the outside shot of the hospital, just before Mort discusses his cough with Doc Hazlet, you can see a sign saying the hospital is located in Ohio, not in Maine. This isn't the only episode where this exact mistake is made.
Factual error: Celestial navigation can determine one's position on the earth's surface to within about one mile, not precise enough to give the location of a buried treasure. It also requires more than a sextant. It requires tables published in a nautical almanac (which is updated each year), charts on which to plot lines of position, and an accurate chronometer that is set to the precise time at the Prime Meridian (Greenwich Mean Time).
Factual error: When Buck's body is found, his blood is red when it should be brown due to oxidation after how much time has passed.
Continuity mistake: When the episode begins, Jessica is having a meeting with Sally Wilson, who hangs a bag over her shoulder. A shot later, her bag is down and she is hanging it again.
Audio problem: When Buck walks to the bar downstairs and meets Mrs. Oates, the sound of their footsteps is that of tiled floor, but they're walking on a rug.
Visible crew/equipment: After Seth drives Jessica downtown, lights, crew, and filming equipment are reflected on the car window.
Continuity mistake: When Jessica is having dinner, his glass swaps between full or almost empty depending on the shot.
Audio problem: Several times during the episode, when someone is walking on a rug, the sound of footsteps is that of a hard tiled floor.
Answer: In a flashback scene, it was shown that he had a violent temper, so it stands to reason that he finally killed her in a fit of rage.