Are there any quotes in Pride and Prejudice that says Mr and Mrs Gardiner have a successful marriage?
I think their marriage is deemed to be successful because of how different their marriage is from Mr. and Mrs. Bennet’s. In Chapter 42, there is a discussion on how Mr. Bennet has basically married a pretty face, but sadly his wife did not possess any of the characteristics to make their marriage a warm and happy one. Later in the chapter, as Elizabeth and the Gardiners are leaving for their trip, the Gardiners are described, seemingly in contrast, “The Gardiners stayed only one night at Longbourn, and set off the next morning with Elizabeth in pursuit of novelty and amusement. One enjoyment was certain—that of suitableness of companions; a suitableness which comprehended health and temper to bear inconveniences—cheerfulness to enhance every pleasure—and affection and intelligence, which might supply it among themselves if there were disappointments abroad.” Directly opposite from Mrs. Bennet, and, presumably, all the better for it!