Reference for Arakhin 10:20

<big><strong>גמ׳</strong></big> ת"ר בני ישראל מעריכין ואין העובדי כוכבים מעריכין

It is because Scripture has included more among those subject to valuation than among those fit to evaluate; for a deaf-mute, an imbecile and a minor each may be made the subject of a valuation, but is not fit to evaluate.

Jastrow