Possible Clues:

• A bit of business that is not for beginners
• With them there's no vice at all
• A bit of the business that's only for the experts
• for the initiated, Father goes back a step
• Such a bit of business is only for the initiated
• One department is not for the uninitiated
• One part of the business is for experts only
• They are very skilful
• A short bit of business is what they're good at
• A little of business is for those with experience