When you “deal in” something you are in the business of buying and selling things.
*The new shop around the corner deals in stolen goods.
When you “deal someone in”, you are permitting the individual to take part in something.
*No way! I don’t think we should deal Laya in.
When a book or an article “deals with” something, it is about a particular subject.
*The book deals with the spread of AIDS.
The expression can also be used to mean, “to manage someone or something”.
*There must be a way to deal with this problem. *Bala finds it difficult to deal with Ganesh.