I think you may have done all that you can at this point. You might just have to wait for him to wise up or fail, and ask you for your assistance.
I used to design and build decks as a side job. I designed and helped build both of my neighbor's decks. When a third neighbor asked for assistance, I worked with him to design the deck he wanted, and myself and the other two neighbors offered to help him build it (our labor free). He declined, saying he would hire someone. He found the worst contractor on the planet. His wife called me on several occasions to come inspect what had been done and advise her/them of any problems. There were tons of problems. His wife continued to call me, but the guy wouldn't ask me, or even want to talk about it. I think he was embarrassed. I knew the county inspector, and worked with him to insure he made the contractor fix all the problems. The neighbor still barely talks to me.