Reference for Bekhorot 57:11

<big><strong>מתני׳</strong></big> הנוטל שכרו לדון דיניו בטילים להעיד עדותיו בטילין

If your argument is true, in the case of an unblemished firstling also it might be said that it is really blemished and the reason why he does not permit it is because he thinks that he might be able to take payment a second time? - The Rabbis enacted payment for the first examination but they did not enact payment twice [for the same firstling].<span class="x" onmousemove="('comment',' There is no fear, therefore, lest the firstling is really blemished and that it is pronounced unblemished in order that the priest might receive a further payment in a subsequent examination as there is no double payment for the same animal.');">⁸</span>

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