Reference for Bava Kamma 168:4
אמרי שור בשור ושור באדם נמי לא קים לן בגויה אלא פוק חזי היכא מזדבני תורא בשוקא אדם באדם ואדם בשור נמי פוק חזי היכא מזדבני עבדי בשוקא
— It may, however, be said that we act as their agents only in regard to a matter of payment which we can fix definitely, whereas in a matter of payment which we are not able to fix definitely [but which requires valuation] we do not act as their agents. But I might object that [payment for damage done] to chattel by Cattle or to chattel by Man we are similarly not able to fix definitely, but we have to say, 'Go out and see at what price an ox is sold on the market place.' Why then in the case of man [injured] by Man, or man [injured] by Cattle should you not similarly say, 'Go out and see at what price slaves are sold on the market place'? Moreover, why in the case of double payment<span class="x" onmousemove="('comment',' For theft. ');"><sup>3</sup></span>