1 Kings 20:4 New International Version
The king of Israel answered, "Just as you say, my lord the king. I and all I have are yours."
There is a nice explanation of this in Pulpit Commentary
Much has been written about Ahab's pusillanimous acquiescence in these disgraceful terms, etc. But it is not absolutely clear that he ever meant to surrender either wives or children to the invader. All that is certain is that he judged it wise, in the presence of the enormous force arrayed against him, to make every possible concession, to adopt the most subservient tone, and to cringe at the feet of Ben-hadad. But all the time he may have hoped that his soft answer would turn away wrath. It is very far from certain that had Ben-hadad sent to demand the wives and children which Ahab here seems willing to yield to him they would have been sent. When Ben-hadad threatens (ver. 6) a measure which involved much less indignity than the surrender of the entire seraglio to his lusts, Ahab stands at bay. Allowance must be made for the exaggerations of Eastern courtesy. The writer was entertained in 1861 by Jacob esh Shellabi, then sheykh of the Samaritans, who repeatedly used words very similar to these. "This house is yours," he would say; never meaning, however, that he should be taken at his word.
There are other examples of these kinds of exaggerations of Eastern courtesy.
Esther 5:3 Then the king asked, "What is it, Queen Esther? What is your request? Even up to half the kingdom, it will be given you."
1 Kings 2
19 When Bathsheba went to King Solomon to speak to him for Adonijah, the king stood up to meet her, bowed down to her and sat down on his throne. He had a throne brought for the king’s mother, and she sat down at his right hand.
20“I have one small request to make of you,” she said. “Do not refuse me.”
The king replied, “Make it, my mother; I will not refuse you.”
21So she said, “Let Abishag the Shunammite be given in marriage to your brother Adonijah.”
22King Solomon answered his mother, “Why do you request Abishag the Shunammite for Adonijah? You might as well request the kingdom for him—after all, he is my older brother—yes, for him and for Abiathar the priest and Joab son of Zeruiah!”
Why did the Elders tell King Ahab not to agree to Ben-Haddad, King of Syria second command?
Because it was obvious to the elders that Ahab didn't mean what he said at Ben-Haddad's first request.