Our groceries shop give 10% for customers who have an account (and thus frequently shop there)
Although this is common and normal practice I just wanted to double check this is not a question of Ribbis, as at times we pay in advance and at times for past (purchased) goods
Kind rgds and thanks
There is no problem, as the discount is given because you are a repeat customer and not because you are giving him the money in advance.
All the best