Do my parents have the right to an increase in the amount after the currency depreciates? What is the ruling on the action of an agent who violated the instructions of his principal? And what is the ruling on buyers exploiting the economic situation?

The amount due from the buyer is what was agreed upon in the contract. The seller has no right to demand an increase due to a decrease in currency value, unless the currency becomes unavailable in the market, in which case the payment would be made at its value on the due date.

There is no harm in the buyer delaying the deferred price within the stipulated period. A change in currency value does not necessitate accelerating the deferred payment except with the buyer's consent, and the seller does not have the right to revoke the deferment without the buyer's consent.

If the buyer pays the agreed-upon price within the specified period, the seller is obliged to deliver the sold item. This applies to both the agent and the principal.

Scholars have differed on the authority of the sales agent regarding the delivery of the sold item and the collection of the price: - Hanafis: The sales agent has the authority to collect the price and deliver the sold item. - Malikis: The sales agent has the authority to collect the price and deliver the sold item, unless there is a custom preventing this. - Shafi'is: If possession is a condition for the validity of the contract, then the agent has the authority to take and give possession. In an absolute sale, the agent has the right to collect the immediate price and then deliver the sold item, unless the principal prevents it. - Hanbalis: The sales agent has the authority to deliver the sold item, but not to collect the price.

In case of dispute, recourse must be made to the Sharia court or arbitration.