Focusing on some and not a variety of items would depend on the kind of store that you have. For consumer goods especially the common merchandise such as household items I guess it is best to have a variety of products in your shop so that the customer can have many choices to buy. When a customer comes to buy a broom but he sees a dust pan or even a plastic trash bin that can probably remind him that he needs that too so instead of getting one buy you can get 2 buys from one customer.