A: I'm looking to place an order for my company. What's your rate?

B: We charge $X.

A: That's a little high; can you do better?

B: What if I throw in a little something extra, just for you?

A: Oh?

B: Say I give you 1%. Maybe take yourself a little vacation?

This is clearly corrupt. Person A is negotiating on behalf of their company, so any discounts person B offers should be to A's company not directly to A. Yes, A is the decision maker, but they need to be choosing based on what their company needs, not what kickbacks they'll get.

This is exactly what frequent flyer miles are. A business traveler buys a ticket with company money, and the airline passes back a little "thank you" bribe to the traveler for choosing them. Why do we allow this?