Ruling on down payments
Question

                If a buyer and seller agree on a purchase, and the buyer makes a down payment, then later on he changes his mind and decides not to buy, does the seller have the right to keep the down payment and not return it to the purchaser?.
Praise be to Allah.
      Yes, he has the right to do that. This was done by ‘Umar 
      ibn al-Khattaab, and this is the view of Imam Ahmad (may Allaah have mercy 
      on him). 

    Shaykh Ibn Baaz (may Allaah have mercy on him) said: 
There is nothing wrong 
    with keeping the down payment, according to the more correct of the two 
    scholarly opinions, if the seller and buyer had agreed to that and the sale 
    had not been completed. 

    Fataawa li’l-Tijjaar wa Rijaal al-A’maal, 
    p. 49 

    It says in Fataawa al-Lajnah al-Daa’imah, 13/133: 

    Making down payments is permissible; that is when the buyer 
    gives the seller or his agent a sum of money that is less than the price of 
    the goods, after the agreement is made, to guarantee that he will get the 
    goods and no one else will take them, and when the goods are delivered, this 
    down payment is to be regarded as part of the price. If he does not then buy 
    the goods, the seller may take the down payment and keep it, and the 
    transaction is valid, whether he stipulated a time for payment of the rest 
    of the price or not. The seller has the right to ask the purchaser to pay 
    the rest of the price once the transaction has been completed and the goods 
    have been handed over. The fact that making down payments is permissible is 
    indicated by the fact that ‘Umar ibn al-Khattaab (may Allaah be pleased with 
    him) did that. Imam Ahmad said concerning making down payments: There is 
    nothing wrong with it. And it was narrated that Ibn ‘Umar (may Allaah be 
    pleased with him) regarded it as permissible. Sa’eed ibn al-Musayyib and Ibn 
    Sireen said: There is nothing wrong returning the product if he did not like 
    it and giving something with it. With regard to the hadeeth that was 
    narrated from the Prophet  (peace and blessings of Allaah be upon him), 
    saying that he forbade making down payments, this is a da’eef (weak) hadeeth 
    which was classed as such by Imam Ahmad and others, and it cannot be taken 
    as evidence.