What is the ruling on benefiting from the discounts and features offered by e-commerce websites (like Booking.com) to customers when they increase their bookings or purchases, whether it's a free night, discounts, or points that can be used for personal purchases, especially if these features result from bookings or purchases made by the customer for themselves and for others? Is it permissible to exploit these discounts to make a financial profit by selling the product or service at its original price?

It is permissible to utilize the features of free booking websites. Any discount obtained from booking for oneself belongs to you, and whatever is for others belongs to them, unless they permit otherwise.

You may request a fee for making bookings for others (an agency for a fee).

It is permissible to benefit from membership and profit from it by buying at one price and selling at a higher price, provided that the other party is informed that you are profiting. This requires you to be a seller, not an agent.

It is permissible to work as a broker in selling products, provided that the original buyers are informed of the profit gained, or you can be a seller or an agent for a fee.