As GP stated, this is not about (not) believing your employees, this is about risk management. In many cases it is justified - do you really want to run your company based on everything your employees come up with? Sometimes you need to check if their instincts are right, especially for decisions that have huge impact on your business. Price for consultants, while it might seem high to you, is actually pretty low compared to business values. Look at it as a kind of insurance.