What is the ruling of Islamic law regarding the fictitious increase in the price of a property, then misleading the client into believing there is a discount and a special offer, while selling the property at its original price?

It is not permissible to resort to the trick of the seller or sales representative telling the buyer that the original price of the commodity is higher than its current selling price. This is a lie and a deception of the buyer. The Prophet (peace be upon him) forbade al-khilaba (deception), which includes deceiving the buyer. In the hadith narrated by Ahmad from the Prophet (peace be upon him): "...And al-khilaba is not permissible for a Muslim."