Sforno on Genesis 42:3/ספורנו על בראשית מ״ב:ג׳

1וירדו אחי יוסף עשרה, the official selling grain in Egypt did not sell to more than one family per buyer. The reason for this restriction was intended to ensure that the buyers would not resell some or all of what they had bought, thus using what Joseph had stored as a source of enriching themselves.