Reference for Bava Metzia 100:7

בטול מקח לא שכיח

can one always retract, or perhaps only within the time necessary to shew [the purchase] to a dealer or a relative? And should you answer, [if only] within the time necessary to shew it to a dealer or a relative, wherein do a sixth and more than a sixth differ? There is a difference: for in the case of a sixth, [only] the defrauded party can retract, whereas in the case of more than a sixth both can retract.<span class="x" onmousemove="('comment',' That is only if the defrauded party demands a refund. Otherwise, it is altogether illogical to give the defrauder a greater power of withdrawal than he would have enjoyed had the fraud amounted only to a sixth. (Tosaf. a.l. and B.B. 84a s.v. [H]) ');">⁷</span>

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