Question Summary:
Purchasing an item on discount by lying to the retailer?

Question Detail:

Please consider the following: Zaid buys some item from Amr, whilst lying to him that he is buying it for a madrasah in order to get a discount. So he is given a discount and pays 600 instead of 800.
Thereafter, Bakr buys the same item from Zaid for the cost of 600.  Now Bake feels guilty.  Was it permissible for Bakr to buy the item? Can he use it for himself?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh. 
If Zaid purchased the item from Amr, Zaid is the owner of the item.  Subsequently, if Bakr purchased the same item from Zaid, that transaction is valid and Bakr will be the new owner of the item.[i] 
If Zaid deceives Amr, he has committed a sin for which he must make tawbah.  However that deception does not invalidate his deal with Amr or with Bakr.     
And Allah Ta’āla Knows Best
Mawlana Faraz Ibn Adam,
Student Darul Iftaa
Leicester, United Kingdom 
Checked and Approved by,
Mufti Ebrahim Desai.
www.daruliftaa.net