I think the problem here is that the realtor is making demands on the homeowner that s/he has no right to demand. The lockbox should be removed if the homeowner wants it removed.
You are right...
but based on the OP's theatrics, I suspect that the agent's version of the story is going to be something along the lines of:
OP: I want you to take the lockbox off, I'm THROUGH with you!
Agent: Ok, but you're going to be responsible for $1,500.00 for breaching the contract.
OP: Oh, HELL NO. There's no way I'm going to pay you anything!
Agent: We'll come take off the lockbox and bill you.
OP: Don't you come NEAR my house!