When the men of the place asked about his wife, he said, “She is my sister,” for he was afraid to say, “my wife,” thinking, “the men of the place might kill me on account of Rebekah, since she is beautiful.”
<citeGenesis 26:7 (NASB)
One reason the rabbis suggest the men of Gerar never kidnapped Rebekah is because she wasn't, in fact, "beautiful."
The Hebrew word here is טוֹב (tov). It means GOOD, but is sometimes translated as beautiful.
Sarah, in Genesis 12, is יָפֶה (yafeh), which is always BEAUTIFUL.