By
The rule of law is that unless the witness be interested in the event of the suit, he shall be admitted; except in those cases, which upon their own circumstances, have been differently established by solemn decisions.
This witness is directly interested in the event of the suit, since his commissions must be measured by the amount of the recovery against the defendant, which therefore he is concerned to enhance. The case cited from Wilson is an exception to the general rule arising from necessity and the usage of trade; the factor is concerned both for the vendor and vendee, and his testimony may be resorted to by both parties, in case of any dispute. He is an agent by whom alone the sale can be proved; but the collector is not necessarily acquainted with the fraud, much less is he exclusively so, since other witnesses have already spoken to it.