Reference for Bava Metzia 144:10
<big><strong>גמ׳</strong></big> אמר ר' אסי אמר ר' יוחנן אין פוסקין על שער שבשוק אמר ליה ר' זירא לר' אסי אמר ר' יוחנן אפי' כדורמוס הזה אמר ליה לא אמר ר' יוחנן אלא בשוק של עיירות דלא קביעי תרעייהו
R. Zera questioned R. Assi: Did R. Johanan rule thus even of a great fair?<span class="x" onmousemove="('comment',' That one may not contract at the market price ruling in great fairs, though such are generally stable, and a fair indication of value. — Durmos, the word in the text, is a disguise of [G], or Mercurius, the divinity of commerce to whom a great annual fair, probably of Tyre, was dedicated (Jast.). [Krauss, Lehnworter, connects it with the [G], race-course, which was also the market-place.] ');"><sup>19</sup></span> He replied: R. Johanan referred only to town markets, where values fluctuate.<span class="x" onmousemove="('comment',' Lit., 'are not fixed.' ');"><sup>20</sup></span>