I took a friend to the local mall because she does not drive. She then proceeded to ask me if I wanted a certain fragrance I was smelling. I really didn't want to accept, but she insisted. What should I have done?

Simply say "Thank you" :)

That is what your help is worth it to her. She wants to show her appreciation. You may accept the gift. If it becomes a habit, then you need to talk her out of it, because help does not need to be purchased.