I have not read all 6 pages but I have a suggestion that I hope might help. Get an empty, dry plastic water bottle. Put a quarter to half a cup of dried beans in it and put the lid on it. When the dog charges at you, shake the bottle, HARD. It should startle the dog, stopping the bad behavior. Say Good boy and go about your business. Don't otherwise engage with the dog. Keep an eye on the dog as you turn to leave. If the dog charges at you again, turn and throw the bottle near him, HARD. (Near. Not at. You don't want to hit the dog.) Calmly retrieve the bottle and walk away. Good idea to tell the dog's owner ahead of time you are going to do this. Do not otherwise engage with the dog on this occasion.
The next time you go in, prepare to repeat. But if the dog stands and does not approach you, smile and calmly, quietly, say Good boy. That's all. As you leave, prepare as above. If dog does not charge you, quietly say, Good boy. And leave.
Repeat for about three days. When you are sure the dog will not attack you, you can calmly, quietly offer to pet him as you enter and leave.
If you try this, I would appreciate feedback on how it works for you. You should not have to fear getting bitten. Nor should you have to train somebody else's dog. But this is pretty much self-defense and I'm confident it will work.
