Or HaChaim on Genesis 42:10/אור החיים על בראשית מ״ב:י׳

1 ויאמרו אליו לא אדוני, They said to him: "No sir, etc." They said; 1) There is no reason to suspect us of spying even if we had come without a specific purpose. [I believe the author derives this from the tone-sign tipcha under the word באו; we would have expected the tone-sign mercha Ed.] 2) "In fact your servants have come to purchase food." They presented the purpose of their presence to buy food as the most natural explanantion for their journey to Egypt.