I have enjoyed using Zuji for various things.
Have only changed tickets twice I believe.
Case 1) Was shifting Domestic J tickets. No fee charged.
Case 2) Actually convinced QF to change my J tickets. Once again, no fee charged.
As I've said before, the Zuji fee seems to be an optional fee from them. When it applies, I'm not sure. But assume it's when you really annoy them!
Have only changed tickets twice I believe.
Case 1) Was shifting Domestic J tickets. No fee charged.
Case 2) Actually convinced QF to change my J tickets. Once again, no fee charged.
As I've said before, the Zuji fee seems to be an optional fee from them. When it applies, I'm not sure. But assume it's when you really annoy them!