Reference for Bava Metzia 161:14

הנהו אהלויי דכל יומא הוה אפי לה חד מינייהו ההוא יומא אמרו ליה לחד מינייהו זיל אפי לן אמר להו נטרו לי גלימאי אדאתא פשעו בה ואגנוב אתו לקמיה דרב פפא חייבינהו

but exempt if on the return journey, because he is regarded as a paid bailee.<span class="x" onmousemove="('comment',' [Since he has no longer any intention of buying them, the goods cannot be accounted any more his property, and his liability can arise only in consequence of the goodwill he enjoyed, which makes him rank as a paid bailee, even though the tradesman had actually received payment for this benefit. How much more should this be the case with a gratuitous borrower.] ');">¹¹</span>

Jastrow