Is it obligatory to inform the pharmacist that the medicine is Chinese, knowing that it contains the same active ingredient and form, for the purpose of realizing a greater profit? And what should the seller do concerning past transactions if the answer is that notification is obligatory?

If the quality and price of products differ, then the pharmacist's failure to inform the buyer of the true nature of the product is considered forbidden deception, which grants the buyer the option to either uphold or annul the contract. The repentant seller must seek absolution from the pharmacists with whom he dealt, or return the price difference to them if they were unaware of it. If returning the price difference is not possible, he should donate it as charity on their behalf.