If you feel the need to do so, make it clear that even though no money was exchanged, that you feel that people need to know that this person is a flip-flopper, and wasted your valuable time.
I don't see why you shouldn't do it, if that is what you'd like to do. Just make things crystal clear about what happened, and prepare to defend yourself if questions arise.
Some people don't think that it would be BOI worthy... It is on you to decide.