(MONEY Magazine) – John D. Rockefeller once said that "a friendship founded on business...is a good deal better than a business founded on friendship." He might have added: "Except in real estate." That's because some of the most successful real estate companies have started as alliances of friends and family. Orange County, Calif. megadeveloper the Irvine Company was created in the 19th century by James Irvine and his son. Donald Trump's dad Fred taught his Apprentice plenty about the family biz. Chicago real estate guru Sam Zell credits much of his success to his longtime partnership with his college pal, the late Robert Lurie. (Old John D.'s spawn didn't fare too badly either with a family venture in the 1930s called Rockefeller Center.)

To be sure, if you're just starting a real estate project, you'll find it difficult to resist the temptation to bring in friends and family as partners and investors. After all, those are the people you know and probably trust the most. But how do you avoid the seemingly inevitable "Dallas"-style dramas?

1 TRUST BUT VERIFY

Even if she's your sister or cousin, you should investigate a would-be partner's finances before doing business with her. Handy websites like Intelius.com and Public-records-now.com can help you unearth basic background info like tax liens or bankruptcy filings. Ask her to share a copy of her latest credit report. Talk to her former business associates. To avoid ill will, tell her from the get-go that you'll be prying--and invite her to do the same with your background. If she balks, calmly explain that such precautions will only make for a stronger team, suggests Nicole McAllister of the University of Southern California's Lusk Center for Real Estate: "Remember, this is business."

2 SHARE A VISION

It's critical that you and your partners agree to common goals before you buy. Will you renovate that apartment house to a level that would make a Hyatt Regency manager blush? Or do you want to rent the property "as is"? Is the goal long-term cash flow or cashing out quickly? Many partnerships founder on these simple points.

3 GET IT IN WRITING

Lawyers and their contracts can't prevent every calamity, but a written agreement--think of it as a prenup before your partnership marriage--can prevent headaches (and heartaches) for you and the family or friends who invest with you. At the very least, an operating agreement will force you to plan for the unexpected, including death, divorce or a change of mind. You must also spell out exactly what happens if one of your partners wants to sell. Establishing a contingency plan "gets everything on the table," says Philip Davis, a C.P.A. and principal at accounting firm Kauffman & Davis in Boston. "It's like going to a therapist."

4 HIRE STRANGERS

Unbiased advice is essential for all involved. Brooklyn real estate broker Tammy Shaw knows plenty about the business, but she says she'd never have bought her brownstone with family without professionals at her side. "Build a team ahead of time--an attorney, mortgage broker or banker, and contractor," she suggests. "They have to be people all of you feel comfortable with."

5 BE AN OPEN BOOK

Garry Klein, co-founder of real estate fund Highpoint Equities in Scarsdale, N.Y., knows both the hazards and huzzahs of working with friends and family. He started buying real estate nearly a decade ago with his buddy Jeff Gault; family members have been a big source of capital ever since. "The upside is that these people know you and know what you're about; they cut you more slack," he says. "The downside is these are people you're going to see at Thanksgiving dinner." Klein shares thorough, detailed investment results every six months.

Ultimately, success depends on your own ability to find good deals and execute. Friends and family can make a newcomer feel more comfortable, but you'll need to adopt professional practices for your effort to really pay off.