BT BM 51a(34) :מידע ידע כמה שוי זביניה והא דזבניה הכי משום זבינא דאתרמי ליה אחולי אחיל גביה‏ : he knows quite well how much his merchandise is worth, and the reason that he sold it thus [i.e. cheaply] is because of (other) merchandise which he chanced upon and he completely relinquished in its favor
See the entire entry for zḇīn, zḇīnā n.m. purchase