Steve Michell had one of the best credit scores in America. But he wanted a perfect 850.So the 52-year-old Texan started tinkering with his 840s score. He followed tips on his banking app, then came to believe they were bunk. He closed credit cards, tweaked balances and adjusted when he paid his bills. He would make a change, then wait a month to see how his score rose or fell. He adjusted again. He waited again.