How does one's profession affect the validity of their testimony?

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Professions considered base and avoided by those possessing Muru'ah, such as emptying cesspits ('kannas'), invalidate testimony. This is based on reports involving Ibn 'Umar and Ibn 'Abbas regarding those involved with refuse. However, for professions such as sweepers of refuse ('zabbāl'), tick removers ('qarrād'), and cuppers ('ḥajjām'), there are two views: one holds that their testimony is invalid due to the profession's baseness, and the other accepts it due to public necessity. If accepted, it is conditional upon their purification for prayer at its appointed time. Trades such as weaving, guarding, and tanning are considered superior, and the testimony is not rejected based on the profession alone. Testimony is not invalidated by other professions lacking baseness, unless the person habitually swears falsely, breaks promises, consistently delays prayer beyond its time, fails to cleanse themselves of impurities, or if their profession itself is forbidden, such as makers of musical instruments (flutes and lutes). If a goldsmith or money changer's trade frequently involves usury and they do not abstain, their testimony is rejected.