If he cant keep up on his end of the bargain starting with the down payment and then again on the second payment he will not get any better.
He has no money and is a liar.
You should just give him his money back and forget about the deal before he really pisses you/your dad off.
I just did head gaskets for a friend, she gave me $500 and owed $200 and said I would get it Monday( one week later) I said OK.
Two weeks after the due date I text her and say WTF, where is my money.
She responds "Do you really need it now?"
I respond "Yes my dogs need to eat" lol
She brought me my money a few days later and tells me she had this and that bill due and she was off work for a week. Why is it my problem?
Be a man of your word and pay up! Or GTFO!!!!