Commercial value and legally required equality are different tests. Better quality may command a higher market price, but direct ribawi barter within one genus is governed by its recognized quantity measure rather than an estimated difference in value.
For instance, 1 kg of purer silver cannot be directly swapped for 1.2 kg of lower-grade silver simply because the parties consider their prices equal. Weight equality remains necessary for silver against silver.
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Riba: Operative Causes, Unequal Exchange and Deferral
Commercial value and legally required equality are different tests. Better quality may command a higher market price, but direct ribawi barter within one genus is governed by its recognized quantity measure rather than an estimated difference in value.
For instance, 1 kg of purer silver cannot be directly swapped for 1.2 kg of lower-grade silver simply because the parties consider their prices equal. Weight equality remains necessary for silver against silver.