Buying and Selling: A Buyer's Intention Not to Pay
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 2073
If a buyer seriously intends to engage in a transaction but his intention (qaṣd) is to not pay for the item that he is buying, this intention does not affect the validity of the transaction. However, it is necessary for him to pay the seller for the item.
-Ayatullah Sistani, Practical Laws of Islam, Buying and Selling