Or HaChaim on Genesis 34:16/אור החיים על בראשית ל״ד:ט״ז

1 ונתנו את בנותינו לכם, "and then we will give our daughters to you, etc." Here the brothers displayed great astuteness. As a rule, swindlers prefer to be very vague when describing the conditions under which they enter into commitments; not only that, but they usually leave the other party many loopholes in order to lure that party into entering into the desired contract. The sons of Jacob reversed this procedure in order to remove any doubt from the people of Shechem that they were being tricked. They offered their daughters in marriage without reservations and explained that as a result they themselves would marry the local girls. All of this was designed to convince Chamor and his people that their intentions were honourable.