You or your agent cannot show house without seller's approval.

Before the deal is closed, your agent need permission from seller every time he enters the house. You cannot even enter the house if your agent is not with you.

You cannot take any application fee, deposit, or check candidate's credit before deal is closed. You are lucky that the candidate refused to give you deposit. If you took his deposit, you are really in deep trouble. That will be enough to be a fraud crime.

For now, I don't think you are in deep trouble. The guy is a jerk. Just ignore him. Let him do whatever he want to do. You and your agent will just have to deal with the consequence it the jerk did file something. Learn it as a lesson.