re: Property Tax Situation

Well you hold all the cards. He'll likely never know unless you tell him. If you are going to try and give him some back, just explain the situation and tell him you think you are entitled to retain X% of the difference because the work you did. If he was entitled to $4800 and you are offering him $2400, its probably not worth his time and money to file suit over the difference. No attorney I know is going to want to get involved in that either.