Deposit one client payment into your personal checking account and a judge can treat your LLC like it never existed. Lawyers call it commingling. Last year 5.67 million Americans filed paperwork to start a business, and a huge share of them ran the first month of revenue through the same account that pays their rent, because the business account didn't exist yet. An LLC protects your house because the law treats the company as a separate person from you, and courts only honor that wall if you…