Revealing mistake: In the scene where Ashley is brought back wounded from the raid where Scarlett's husband Mr Kennedy was killed, Melanie grabs an oil lamp to follow the man carrying Ashley to the bedroom and you can see an electrical cord hanging down from it. (00:50:45)
Continuity mistake: When Aunt Pittipat serves her last Madeira Uncle Peter is standing on her left. Then the camera angle changes to a close-up on her, and in the next wide shot Uncle Peter is standing on her right. (00:52:00)
Continuity mistake: When Scarlett talks to Ashley about eloping to Mexico at some point she turns away from him. This move is seen from two angles, where in one her scarf covers one shoulder, in the other both. (00:18:15)
Continuity mistake: When Rhett picks up Melanie from her bed to take her out of Atlanta he is not wearing a hat, but in the next shot it is on his head. (01:19:35)
Continuity mistake: When Scarlett's father comes home to announce that the war is over Melanie is standing on the stairs with empty hands. When we see her next a moment later she is carrying her baby. (00:09:15)
Answer: If she looked rich she could trick him into thinking she wasn't marrying him for his money.