Shine, I would change one thing you said. Don't choose your painter by how much he needs up front. If he has a good reputation, (and you better check him out good), that will be a pretty good indicator of his reliability.

I am a full time painter, who has been painting for 40 years. I ask for half, to two thirds down, on a job. I'm not broke, and I will last through any job. It's just that I am not willing to wait weeks to be paid anything on jobs that can run hundreds of hours. I also don't care to pay $1000-$2500 for someone else's materials either. I wouldn't ask that of them.

You are absolutely right to question their reliability and also their honesty. Painters are people, and as you know, some people are not great human beings, but don't let the amount of the deposit keep you from hiring the best guy for the job.