Adam Clarke on Genesis 29:15

Because thou art my brother, etc. - Though thou art my nearest relative, yet I have no right to thy services without giving thee an adequate recompense. Jacob had passed a whole month in the family of Laban, in which he had undoubtedly rendered himself of considerable service. As Laban, who was of a very saving if not covetous disposition, saw that he was to be of great use to him in his secular concerns, he wished to secure his services, and therefore asks him what wages he wished to have.