Or HaChaim on Genesis 29:15/אור החיים על בראשית כ״ט:ט״ו

1 ויאמר לבן..הכי אחי אתה, Laban said: "Because you are my brother, etc." Who had told Laban that Jacob would serve him for free? Assuming that Jacob indeed did not ask for wages, so what? Why should it bother Laban? If Laban did not want to become the beneficiary of gifts, i.e. שונא מתנות יחיה, this is most unlikely as we see Laban enjoy even stolen goods. He must certainly have been willing to accept legitimately acquired gifts willingly!

2Surely we must understand his question as one that was designed to pay Jacob less than his labour was worth. Maimonides writes in Hilchot Shluchin VeShutafim chapters six and eight that when a shepherd has not made an agreement with the owner of the flock before he accepted the position he receives one third of the profit of stationary goods (items that do not need his special daily care) and two thirds of mobile goods such as calves and young asses which need to be fed, etc., by the shepherd. Laban was afraid that Jacob's silence on the subject of wages indicated that he expected to be recompensed according to this rate. He thought Jacob expected to receive one third of the increase of the adult animals and two thirds of any increase in the ones not yet fully developed. Laban would have been quite right to continue to let Jacob work for free if the latter had been the average fool not bothering to make a contract. However, since Jacob had already spelled out to Laban that he was no fool, i.e. that he was just as capable of tricking Laban as the latter was in the habit of tricking others, he told him we have to make an agreement precisely because "you are my brother (in the art of trickery)." He challenged Jacob by saying "surely you do not want me to believe that you will work for me for free?" Laban therefore wanted to clarify at once what conditions Jacob expected him to meet.