Question Summary:
Extra discount of 10-15% if bought through a certain banks debit/ credit card.

Question Detail:

Assalamu alaikum. I'm from India. Here when we buy any product online the vendor give us an extra discount of 10-15% if bought through a certain banks debit/ credit card. Is this kind of purchase permissible? Vassalam 

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
The discount offered by the vendor is permissible.[1]
 
And Allah Ta’āla Knows Best
Imran Patel
Student Darul Iftaa
Lusaka, Zambia. 
Checked and Approved by,
Mufti Ebrahim Desai.