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For each major role in your company, there's a single job interview question that outweighs everything else. How the candidate answers that question -- and not the answer itself! -- should determine if the candidate will be a help or a hindrance.

Here are the essential interview questions for five key jobs.

1. Hiring a manager.

Key question: "What is a manager's most important task?" 
What to listen for: Whether the management style matches your needs.

There are three basic types of manager: 1) coordinators who guide employee behavior, 2) coaches who develop employee skills, and 3) bureaucrats who play politics.

Coordinators believe that "achieving goals" is the most important task. They're most useful when a situation is chaotic and in flux, as when a company is growing very quickly.

Coaches believe that "improving behaviors" is the most important task. They're most useful for established teams that aren't performing up to their full potential.

Bureaucrats believe that "managing numbers" is the most important task.  They are useless for anything except playing politics. Avoid them like the pox.

2. Hiring a marketer.

Key question: "What's the relationship between 'sales' and 'marketing'?" 
What to listen for: Any hint of disrespect for salespeople or the sales process.

Marketing has two important tasks: 1) generating qualified sales leads and 2) providing tools to help salespeople turn sales leads into paying customers.

Marketers who don't respect salespeople inevitably generate sales leads that the sales team can't close and sales tools that salespeople don't want.

Therefore, if you hear anything like "marketing sets strategy and salespeople execute tactics," do not hire that candidate.  If you hear something like "marketing is a service that helps salespeople sell," you've got a winner. 

3. Hiring a salesperson.

Key question: "How do you define 'selling'?" 
What to listen for: The flavor of the words the candidate uses.

Candidates who use manipulative terminology like "convince," "persuade," and "compel" will take a hard-sell approach. They'll try to badger even unqualified prospects into becoming customers.

Candidates who use relationship-based terminology like "ask questions," "listen to," and "help" will take a solution-sell approach. They'll find ways to make both your company and the customer successful.

If want to generate revenue quickly and don't care whether customers get screwed, hire the hard-seller.  If you're in business for the long haul, hire solution-seller.

4. Hiring an engineer.

Key question: "What constitutes 'good design'?" 
What to listen for: Evidence of engineering dogmatism.

The best engineers tend to think about design as the process of adapting products and services to the needs of the people who are destined to use them.

The worst engineers tend to think about design as building something that makes sense to themselves, and that users should learn to think like engineers.

Hiring engineers who get that design goodness is all about usability will result in products that customers buy and love; hiring dogmatists... not so much.

5. Hiring support personnel.

Key question: "Describe a situation where you felt rejected." 
What to listen for: The emotional resiliency to stay upbeat and positive.

Support jobs always involve dealing with other people's emotional baggage.  Admins, for example, must deal with stressed-out execs; customer-support folk must deal with constant anger and abuse.

Because of this, support personnel are most effective when they don't bring their own emotional baggage into the situation. They need to remain helpful without owning the other person's opinions.

Ultimately, this means the ability to deal with personal rejection without taking it to heart. So you're looking for somebody who can "take it" without feeling the need to "dish it out."