Brother, I get it. But as hard as it is. You might have to check some ego. Some fights are not worth it. Wrestling with a pig comes to mind. I have the same mentality so does my brother. You learn quick that we have a “legal system” not a “justice system” it will likely cost more than 4k and you will have nothing to show for it other than stress and bills. ( well I would wish it on the POS who stiffed you) I would not wish that on anyone. I think you get a collections company to hound him and or small claims court, it will be a giant PITA for him and if you have good proof will likely go your way and you won’t just be paying a lawyer