Posul for Eidus Due to Financial Interest and Aveirah

Some eidim are posul due to financial interest, i.e., when someone derives benefit from serving as an eid (Choshen Mishpot 37:1). Based on this, the poskim go through various people to determine whether they are posul as eidei kesubah and kiddushin:

• Shadchan - Some are machmir not to use the shadchan as an eid since he has a financial interest (Yismach Lev, Vol. 1, siman 163; Apiryon Shlomah pg. 63 in the name of R’ Yaakov Kamenetsky; Teshuvos HaPoskim in the name of R’ Chaim Kanievsky zt”l). However, others hold he is only posul as long as he was not yet paid, but once he was paid, he is kosher l’chatchilah (Otzar Haposkim 42:65, ois 15 in the name of the Maharit; R’ Elyashiv cited in Mevakshei Torah).
• Mechutan - Strictly speaking, a previous mechutan is kosher for eidus (Shulchan Aruch, Choshen Mishpot 33:6; Rema, Seder Haget 2; Maharshdam, siman 33 and Aruch HaShulchan 5). However, some are careful l’chatchilah not to use a mechutan as an eid kiddushin since it is possible that there is always some financial interest between them even if they became mechutanim a long time ago (Peninei Nisuin pg. 68 in the name of R’ Elyashiv; Kovetz MiBeis HaLevi, Vol. 9, pg. 33).
• Mesader kiddushin - The mesader kiddushin may be an eid kesubah or kiddushin even if he will be paid (Shu”t Binyan Tzion, siman 157).

Posul for Eidus Due to Aveirah

• Desire for money - A person who does aveiros out of desire for money, e.g., someone known to be a thief, is posul de’O’raisa for eidus. A gambler is posul derabanan (Shulchan Aruch, Choshen Mishpot 34:7).
• Rasha - A rasha who knowingly violated a lav from the Torah that all Yidden know is an aveirah and did not do teshuvah is posul for eidus (34:1). However, if it is possible he did it by accident or did not know it was forbidden, he is not even posul derabanan for eidus (Shulchan Aruch 34:2; Shulchan Aruch HaRav, Dinei Eidus Veshtoras, sif 7). For an aveirah that does not get malkus, one is posul miderabanan (Rema, sif 3).
• Suspected of arayos - If someone is even just suspected of arayos, although he is kosher for other eidus, he is posul for marriage-related eidus (Tur Choshen Mishpot, 34:25 and Rema), at least miderabanan (Chelkas Mechokek 45:14; Beis Shmuel 45:20).
• Technology - To our great distress, there is a spiritual disaster today with the development of technology. If a person has access to unfiltered internet, it is impossible to know that he isn’t suspected of arayos, particularly if he has any sort of unfiltered smartphone that accompanies him around the clock, including in secluded places. It is almost unavoidable that such a person will see forbidden sights and violate the lav of “לא תקרבו לגלות ערוה,” which includes speech and personal connections with every evil in the world. All the rabbanim worldwide have denounced this and forcefully expressed the obligation to guard one’s neshamah from it.