The story of Avraham Avinu asking Sarah to say that she was his sister, is troubling.
On the one hand, we should expect that Avraham would be a man of truth, and not need to do such subterfuge. But on the other hand, perhaps he was teaching that when dealing with people of low moral standards, one needed to outsmart them.
There is an explanation that according to Noachide law, there was no such thing as divorce. Couples simply agreed to go their own separate ways, and were no longer considered husband wife. Their relationship was no longer intimate as husband and wife, and they were now like a brother and sister.
There is a Midrash that says that Pharoah the city of Goshen to compensate her for their misunderstanding. This was the very place the Jewish people lived, when they later went down to Egypt.
The end result of the incident did not indicate that Avraham and Sarah acted wrongly. Sarah was given a city, and Avraham left with great wealth.
The Torah wrote that good things came to Avraham because of Sarah. It was meant to be a reminder that husbands must realize that their success depends on how well they treat their wives.
We are meant to learn from Avraham, what is the behavior of a Tzaddik. We see it in practice and not in theory. We cannot be foolish when dealing with unscrupulous individuals. We need to outsmart them!