Why are they asking you - do they expect to pay full fare, discounted or freebie?
I have a relative who owns a restaurant, I go there frequently - I pay full fare, as expected. I go because I happen to like the food.
I have another relative who is an architect. I asked him to draw me up a set of plans for a SFH I am rehabbing. I expected to pay full price - but didn't pay a dime. This relative I had done some work for and he INSISTED I charge full price, I protested, he insisted. His logic had something to do with "not owing anyone a favor" - but then he broke his own rule when I needed the plans. Maybe he figured I cut him a break on the job I did for him (which I did - but didn't tell him)?
The only people who fly for free with me are my parents and my mother-in-law.