Is it obligatory to refund the price of a car after discovering its VIN was forged and it had been used by several parties, bearing in mind that the car lost its real value six months after the sale?

If the fraudulent astrological number prevents the change of the car owner's name or its sale, then this is considered a defect that gives the buyer the right to return the sale and reclaim the full price without any deduction for usage.

If the car becomes defective while in the buyer's possession: if the defect is minor, it holds no value. If it is moderate, the buyer is given the choice between returning it and reclaiming the price, or keeping it and taking compensation for the old defect (arsh al-'aib al-qadim), which is calculated by evaluating the car as sound and as defective on the day of sale, and determining the percentage of reduction. However, if the defect is major and renders the car unfit for its intended purpose, then the buyer must take compensation (arsh).

The above also applies to the relationship between the buyer and the original seller. That is, you have the right to return the car or demand compensation from the seller from whom you bought it, if the car is returned to you or compensation is demanded from you, unless a new defect occurred while it was in your possession.

A condition for returning due to a defect is that the buyer must not accept the sold item after becoming aware of the defect. Exploiting the sold item after knowing about the defect is considered acceptance of it, unless the exploitation occurs during the time of dispute and does not diminish the value of the item.

Therefore, if the buyer exploits your car after becoming aware of the defect, he does not have the right to return it because of that defect.