The Equal Testimnoy of Females and Males
Whenever a classical text is studied with a lens which is unduly critical, mistrusting and with a biased theological axe to grind, questionable allegations against the text will inevitably result.
In front of God, the witness of one man is equal to one woman. This is clearly attested in cases such as charges of lewdness / slander where no other witnesses are present (Quran 24:6-9). Other witness requirements in the Quran show no preference for gender.
The fact that in Islam, men are expected to be the primary breadwinners is difficult to dispute from the Quran. This can be deduced from the inheritance laws and the way it is structured (Quran 4:11, 4:12, 4:176), the requirement for the dower (Quran 4:24), the expectation of men to support their young after divorce (Quran 2:233), to provide their women with a fair provision upon divorce (Quran 2:229, 33:49) and clearly evidenced by the statement "wa'bima anfaqu min amwalihim" (because they spend from their wealth) when in reference to the general maintenance of women (Quran 4:34).
Therefore, men would be more likely to be engaged in financial transactions including dealing with matters of inheritance. This can be clearly seen in verse 5:106 where the requirement of two male witnesses has been stipulated in the matter of bequests. The Arabic 'ithnani dhawa' is clearly in the dual masculine case and therefore clearly implies 'two men'.
Keeping the above in view and the fact that men in Islam (and generally in antiquity) were the primary sources of financial support for the family and engaged in the fuller scope of financial transactions, the longest verse of the Quran which deals with financial transactions can be better understood (2:282). The requirement for two female witnesses is only borne from the nature of the transactions in question and not intended to provide evidence of female inferiority.
Furthermore, it is important to appreciate that albeit two female witnesses are summoned, the second female witness is only present in case the first one cannot provide sufficient witness to the financial transaction. If she is able to, then clearly her testimony would suffice against the witness of one male.
The fact that the second female witness is only present as an aid and not a main witness, is completely unappreciated by many overtly critical to the ancient text. It would be a rather different matter, if the two females had to provide equal testimony against that of a male's testimony. This is clearly not the case from the context of the verse.
It is to be appreciated that the Quran was not revealed in a silo. It was revealed to guide the primary listeners of the Prophetic call and to address the needs of that society in the first instance. Thus, when studying such an ancient text, it is imperative to understand it foremost in its primary context. Any wider guidance outside that context can then be extracted.
To assert on the basis of verse 2:282 of the Quran which deals specifically with financial transactions, the general rule that one male witness is equal to that of two female witnesses finds absolutely no warrant.
Such an assertion takes no account of the primary context in antiquity or the financial responsibility of the male in Islam. Furthermore, it lacks appreciation of the likelihood of males in both antiquity and Islam to be involved in such transactions and the wider narratives of the Quran which clearly suggest that the witness of one male is equal to that of a female.
...Whenever you give or take credit for a stated term, set it down in writing. And let a scribe write it down equitably between you; and no scribe shall refuse to write as God has taught him: thus shall he write. And let him who contracts the debt dictate; and let him be conscious of God, his Sustainer, and not weaken anything of his undertaking. And if he who contracts the debt is weak of mind or body, or, is not able to dictate himself, then let him who watches over his interests dictate equitably. And call upon two of your men to act as witnesses; and if two men are not available, then a man and two women from among such as are acceptable to you as witnesses, so that if one of them should make a mistake (Arabic: Dalal), the other could remind her... [Part of 2:282]
Thus the basis of the rule is that women, being generally less involved in business matters, may be more prone to forget the details of a deal. Clearly, if we know that certain women in a certain society or age have the knowledge and experience in business matters as the average man or be more knowledable, then the intent of the rule may supercede the letter of the rule. "And if he who contracts the debt is weak of mind or body, or, is not able to dictate himself, then let him who watches over his interests dictate equitably."
There are two qualities required from such witnesses (i) Integrity. (ii) Experience and knowledge of such business matters. (2:82)
If the woman as a witness was worth half that of a man, the verse would have stated so clearly. But obviously that is not the case. Women's testimony in all matters are equal to that of a man or even supersedes his testimony as in the case of a wife testifying against her accusation of adultery, Quran 24:6-10. See also, Quran 65:2, 5:106 and 4:6
And Allah knows best