Maksym,
It's impossible to guarantee that a business person is competent, sorry. Just as it's impossible to guarantee that a developer is competent. But there are some things you could look for that would significantly reduce the risk of them being incompetent:
1) Look for relevant education. Does the person have a relevant undergraduate or graduate degree from a reputable college or university? Ask them to show you their diploma, ask them to show you samples of their coursework (homework assignments, graded exams, ...).
2) Look for relevant certifications. I don't know what the specific certifications would be, but I'd assume that there would be some kind of certification program out there.
3) Look for relevant experience. Have this person explain to you how they solved real-world problems for real-world organizations. The work products from those places are probably proprietary so they wouldn't normally be able to show specific examples, but they should at least be able to talk about them. Check their references--contact those people and ask them whether they thought this person really did a competent job. Ask this person how they would approach doing this job for your organization. If their approach sounds reasonable, they're more likely to be competent than if their approach sounds completely unreasonable.
I would personally be very cautious about hiring an IT manager from one of those companies. The problem is that most IT managers got to be IT managers because of their technical skills--not because of their business skills. You have the technical skills already, you probably don't need more of them. You need the business skills. Don't be afraid to look at getting managers from non-technical businesses, it's the business knowledge that's more important to you than the technical knowledge that you already have.
-- steve