Legendary investor Warren Buffett is no stranger to billion-dollar business deals. Regardless of size or scope of a transaction, the "Oracle of Omaha" uses the same research philosophy:

Don't trust forecasts or projections, especially from someone who has a financial interest in making those projections.

Whether you're buying a stock or a house or a business, the chairman and CEO of Berkshire Hathaway advises to do your own research. Don't trust the "experts."

"Don't ask the barber whether you need a haircut," Buffett told the audience at Berkshire's 1994 annual meeting.