Financially independent real estate investors rely on a 'buy box.' Here's what it means and how to use one to build a cash-flowing portfolio.

Mike Zuber focuses on specific criteria for real estate investments in Fresno. Zuber's "buy box" strategy helped him and his wife retire early with rental income. Other investors use buy boxes to ensure positive cash flow. Real estate investor Mike Zuber won't purchase just any property. He's looking for single-family homes with three to four bedrooms in a particular ZIP code in Fresno. Those are just a few specifications that make up his "buy box" — the set of criteria, from location to property ...