Dude, you have to realize what the application is. An exhaust system for your car. Yes I understand we all want everything to be perfect, however what works like it should and what we want sometimes are 2 different things.
Every day shops are welding exhausts on the car with small mig welders. I don't see too many mufflers on the side of the road that fell off, do you?
Unless said friend is charging you an arm and a leg for this welding work, I would shut up and appreciate it. Welding is one common thing that people are very critical to judge before they have tried it themselves. After that their tone drastically changes.
I have been tig welding, going on 8+ years now (mig and stick much longer) and can barely call my self a decent tig weldor. Some days I am just terrible. Some days are fantastic. I have built quite a few turbo and exhaust setups for guys like you. Heck it helped put me through college. Before I ever accepted their work I showed them samples of what the finished welds would look like. That way they knew what to expect when all was said and done. I had ONE guy walk away to only then come back a few months later. Who was then very happy with the finished product.
Technically neither the 2nd or 3rd weld pic is perfect, will it hold? Yea. Out of curiosity what kind of background and experience do your "Friends" have. Are they full time weldors by profession, specifically tig process? Or folks that just recently purchased a machine to fool around with? Reason why I put that in quotes is usually when people find out I have a tig machine at the house they all a sudden become real chummy, with their eyes set on one thing. I am starting to get the impression you may be one of those folks.
Maybe you could both discuss the welds and you both could learn something. A good friend should want to help their friends grow and succeed. Not just walk away when there is a problem. 
