Samantha's Thanksgiving to Remember - S4-E12
Factual error: I noticed a grandfather clock when they all arrived in Plymouth (in the right corner). I won't assume this is the first Thanksgiving since the colony is built up and seems established. Plymouth was from 1620-1690s. I had to research but apparently there would not have been an ornate grandfather clock available. The first clocks were built around the time but were not common - especially in an American colony like Plymouth struggling to survive.
Birdies, Bogies, and Baxter - S4-E7
Other mistake: In the scene at the end where Baxter is saying "You learn something about how you take defeat, I never thought I would be learning something about myself" the background behind Baxter doesn't match the background when the shot is a wide shot showing the out door course, trees and buildings. Instead it looks like a painted backdrop perhaps filmed separately for the closeup. It's definitely not where Baxter is standing in wide shot.
Naming Samantha's New Baby - S6-E6
Factual error: When Mr. and Mrs. Stephens are driving in the convertible. In second shot, there are at least 2 tall palm trees along the road. Morning Glory Circle is supposed to be a NY town. There are no palm trees growing in NY. It's obviously shot along a CA road.
It's So Nice to Have a Spouse Around the House - S5-E5
Continuity mistake: Samantha removes a spell cast by some other witch; it's a series plot point in many episodes that Samantha cannot undo someone else's spells.
Other mistake: This is a remake of season 1 episode when Paul Lynda makes his first appearance as Harold the driving instructor for Samantha.
Suggested correction: This is trivia at best, but the episode isn't really a remake of an earlier episode. Here Samantha teaches Uncle Arthur (Lynde) to drive and in season 1 Harold (Lynde) taught Samantha to drive. But the same actor playing multiple roles in a series is never a mistake.