Honesty and self-honesty are key. Curiosity too. They best business people tend to teach as they go... but the worst like to lecture as they go. So talkativeness is not always a good sign.
Greed in a business person is not fatal, but needs to be watched. Hunger is a better motivator than greed because it's self-limiting.
Business school is not always a good indicator -- I've met both idiots and geniuses who went to Sloan, LSE, EDHEC, etc.
Self-taught or self-made business folk tend to have smaller horizons. You find them a lot in businesses that are less risky, more limited, yet profitable -- eg contract software for government.
Scions of old successful (eg 4 generations) families can be very good as long as they are not too emotionally scarred. If they have something to prove, let them do it somewhere else.
People who have entrepreneurs (parents, aunts, etc) in the family tend to have more natural and secure approach to business overall. They've seen it done from birth.
One good negative indicator is being too "fancy". If a person seems to create complex deals just for the joy of it, run away. You want elegant power in business deals just as you want it in programming. Being too fancy is a sign of inexperience, but may also be a sign of greed or worse.
Another negative indicator: I've never seen a VC make an outstanding CEO.
1. There is a lot of arrogance among business people. They (probably as engineers) think that they know things, that others don't. If you meet someone with an arrogant attitude I would steer away from him. And even if it is only because it will e hard to work with them.
2. Smart. Really good business people are truly smart, but how do you recognize a smart business guy? I have found, that people who have mastered their subject can explain it in very simple terms. They can teach people the reasons behind their decisions and why they are doing something the way they do. And most of the time that explanation (at least in business) will be very straight forward and seem like something that is obvious, but it wouldn't have occurred to many other people and it had to be spotted. it's almost like good business ideas, the best ones often are obvious and can be understood by almost anyone.
3. Good business guys are curious. They are broadly interested and fascinated with a lot of stuff. In the article that spun off this thread the Blogger mentions curiosity and self teaching as important in a good programmer. And I would reiterate that point here. A good or even great business guy probably isn't into business because of business but because of other interests he wants to connect / advance. I for example study business because I am very interested in Technology (IT and classical engineering), Biology, Chemistry and Physics. My interest in business lead me to pick up that for my studies because it makes it possible for myself to later connect my areas of interest through my work. Am I a good business guy? I don't know, but I hope to be one day. But I have seen a lot of good business folk who shared that trait. They start learning about e.g. programming and they will probably never be as good as the experts in such a field but they will start to understand a field and can contribute a sense for business and the business perspective to the field.
4. A good business guy understands the field he works in.
Here's what I told her engineers look for:
Proof that they get shit done. This is the first thing you'd look for in an engineer for starting a company, and it's likewise the same thing you need in a business guy. The definition of what shit needs to get done is very different, but it's still the most important thing. So, what projects have they headed up and gotten done? "Business guys" need to wield the phone, email, project budget, underlings, teammates, etc. in order to make things happen. If they have excuses for why their team or their prior workplace was crappy and held them back, or whatever, they might not have the right attitude.
Be willing to do the stuff that hackers hate. This usually includes business development, accounting, taxes, legal, etc. A lot of talking to people and choosing vendors and service providers, and figuring out ways to get everything cheaply but in a timely manner.
Decisiveness is probably important in a business guy. Not recklessness...just the ability to make decisions in a reasonable time. They need to be a good and quick judge of character, since they'll be making most of the deals...and a bad partner early on can spell the end of your startup.
Likewise, they need to be honest and have character, themselves. There are business guys who get ahead by screwing others, but you probably don't want to work with them (because they'll screw you, too), and unless they're really good at it, in the end it will backfire. The tech industry is, perhaps surprisingly, polite. Competitors are friendly with each other, and very rarely bite each other in anything other than honest ways...because a competitor one day is a partner the next, and the more you grow and expand your offerings, the more this will happen. For startups, a competitor one day may be an acquirer tomorrow, as well. So, don't work with people whose primary competitive philosophy is "screw everybody else". Competing aggressively is obviously mandatory. But, if they'll say anything to make a sale, it's not good for the long term life and growth of your business.
Bring money or the connections to get money. This is crass, of course, and there are lots of other useful things a business guy can bring to the table, but bringing money to the table is an indicator of almost everything else you're looking for in a business guy (either that, or dumb luck). It's probably not possible to have good money from a good investor on the table without a prototype...but if they can arrange a meeting with an angel two weeks later to show off your early stage prototype and get the wheels turning on raising a round, you might have a winner.
Be easy to work with, and willing to learn. In the first few months, there's not much to do besides "make something people want", so they need to be able to be a contributing partner on that task. Design, maybe. Docs, maybe. Getting feedback from potential customers, definitely. Figuring out the data you need to build the right things for the right customers. This one is brute force Googling and making phone calls. Finding out the size of the opportunity (and whether other opportunities could be addressed with the same technology), making an honest assessment of the competition and figuring out their weaknesses, etc.