The Gemora in Kiddushin (6a) says that if a woman would give a gift to someone who is an important person and doesn’t accepts presents from just anybody, she would be receiving enough pleasure from the fact that he receives her gift so that he can betroth her with that benefit that she receives.
The Taz (y.d. 160:8) explains that the reason that he must be an important person is because if he is just a regular person, then the benefit she receives, doesn’t have any cash value to it and therefore cannot create a kiddushin.
The Taz continues to apply this concept to the prohibition against lending with interest as well. If a lender tells a borrower, “I will lend you the money you need on condition that you receive this gift from me” - it depends. If the borrower is an important person, then the lender would be receiving real benefit from the borrower willing to receive his gift, which would create a ribbis (lending with interest) problem. But if the borrower is not an important person, there wouldn’t be any ribbis problem. The Taz clearly understands that if the receiver of the gift is not an important person, we consider the value of the pleasure that the giver has to be worth zero, and therefore it is not a ribbis problem.
However, R’ Akiva Eiger (y.d. 160 on Taz) cites a Ran in Kiddushin who asks based on Levi in our Gemora who holds that chalifin is done with the vessel of the seller, because the benefit that the seller receives by the buyer willing to accept his gift, provides enough benefit to the seller with which to sell the item. Clearly, we see that the seller receives benefit by the buyer receiving his gift even if the buyer is not an important person. This seems to contradict the Gemora in Kiddushin!?
The Ran answers that even if the receiver of the gift isn’t an important person, the giver has pleasure that the receiver was willing to accept, but the pleasure isn’t valued at a perutah. Therefore, in the context of kiddushin where her pleasure must equal a perutah, it only works when he is an important person. But, by chalifin, where the benefit received by the seller need not be worth a perutah, even if the buyer is not an important person, it will work.
R’ Akiva Eiger explains that Rav doesn’t disagree with Levi about this. Therefore, in the context of ribbis, where even a slight benefit that the lender receives from the borrower is a prohibition (although not a Biblical one), even if the borrower isn’t an important person, there would be a problem of ribbis. Based on this, the lender cannot say to the borrower, “I will lend you money on the condition that you receive this gift from me,” even if the borrower isn’t an important person, because the lender will be receiving some minor benefit which is forbidden.