You are right, your contract is with your client and no one else. She agreed to your terms which were very fair - in fact you should have charged for that full set ... then you could maybe have felt better about doing the rebalance for free ... although I only correct any mistakes after the first week FOC ... after that it's down to the client.
I had a client who I did a new set on and they were very odd when she came back. We never got to the bottom of what caused it, she came to me for years and it never happened again. I did the rebalance for free and kept her sweet and she was a very loyal client because of it.
I have to say I'm a typical Taurean - very stubborn. If people behave reasonably to me then I will be more than fair back. But if they come in shouting the odds then they get nowhere ... other than a cold shoulder and invite to the exit!!! And you can say to him that if he wants to get funny then you will counter sue for deformation of character and libellous behaviour.
You have done nothing wrong and he has behaved like a total arse. I'd just feel very sorry for your client that she has to live with a prat like that. I bet she will find it very uncomfortable coming back into your salon. What a foolish man :smack: