Responsa for Bava Metzia 186:2
איתיביה אלו הם אונסין ששומר שכר פטור עליהן כגון (איוב א, טו) ותפל שבא ותקחם ואת הנערים הכו לפי חרב אמר ליה התם בחזני מתא
Abaye protested, 'If so, had he entered the town when people generally enter it [leaving his charges alone], would he still be exempt?' — 'Yes', he replied. 'Then had he slept a little when other people sleep, would he also be exempt?' — 'Even so,' was his answer. Thereupon he raised an objection: The following are the accidents for which a paid bailee is not responsible: E.g., <i>And the Sabeans fell upon them</i> [sc. the oxen and asses], <i>and took them away; yea, they have slain the servants with the edge of the sword</i>!<span class="x" onmousemove="('comment',' Job I, 15: this proves that they are free from liability only for exceptional and unpreventable mishaps. ');"><sup>2</sup></span>
Teshuvot Maharam
A. After the period, for which A borrowed the book, had passed, A's responsibility for the book became that of a hired watchman. Therefore, if, before he fled, A could have hired somebody to save the book, and did not do so, he was liable for its loss. But if this was impossible, he was free from obligation.
SOURCES: Pr. 140; Mord. B. M. 376; Agudah B. M. 152.
Teshuvot Maharam
A. The responsibility of the broker is that of a hired watchman since he took the ring in the anticipation of making a profit. The broker, therefore, must swear that the stone is not in his possession; he must also take an oath as to the value of the stone, and must repay that amount to A.
SOURCES: Pr. 547, 548; Mord. B. M. 359. Cf. Agudah B. M. 127.