Is it permissible to sell an item at a price higher than its wholesale price to a customer brought by a friend, on condition that the friend takes the difference between the two prices?

This issue has two scenarios:

The first: The marketer shows the buyer that he works for the shop owner and has agreed with him on a specific commission for every customer he brings. In this case, there is no harm in him taking the agreed-upon fee, provided that the price of the commodity, with this increase, is within its usual price range.

The second: The marketer shows the buyer that he is an agent for him or a trusted advisor to him. In this case, it is not permissible for him to agree with the seller to take an additional amount, as this involves betrayal and deception of the buyer.