I can understand trying to get money back for the cage, but not for the bird. I'd be okay with paying a high rehoming fee if the bird were coming from a rescue, but not if it were coming from the home of someone just trying to recoup their losses from an impulse pet purchase.
As for rehoming fees, I don't have a problem with them as long as they're not exorbitant. If you put your bird up for free adoption, you're running the risk of giving the bird to someone who does not have the best of intentions. I've seen warnings about this on rescue websites. I guess people wanting to breed birds for profit will take free rescue birds and not give them the life you'd want for them. I suppose if I were offering a bird for adoption, I'd include a reasonable rehoming fee in my ad and then waive it once I actually met the person, just to keep greedy opportunists from responding to the ad. You also want to make sure that the person adopting the bird is financially stable and will be able to provide for it, so you want someone who would be willing to pay some kind of adoption fee instead of needing a bird for free.