Responsa for Bava Metzia 186:8
ועד כמה עד כדי דמיהן והיכן מצינו בשומר שכר שחייב באונסין דהדר שקיל דמיהן מבעל הבית
— It means that he heard the voice of a lion, and so entered. If so, why judge his strength? What could he then have done? — He should have met it with [the assistance of other] shepherds and staves. If so, why particularly a paid bailee? The same applies even to an unpaid one. For you yourself, Master, did say: If an unpaid bailee could have met [the destroyer, e.g., a lion] with other shepherds and staves, but did not, he is responsible! — An unpaid bailee [must obtain their help only when he can procure them] gratuitously; whereas a paid bailee must even [engage them] for payment. And to what extent?<span class="x" onmousemove="('comment',' Is he bound to hire helpers? ');"><sup>7</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.