In the event you want to avoid customer who purchase bulky items from selecting normal postage, you can EXCLUDE the bulky items category (shoes, coats, gift set and etc) from the normal postage.
When you named the category / collection, the shipping method won't available for customer has the said items in their cart.
- From MANAGE YOUR STORE (DASHBOARD), go to SETTING then go to SHIPPING
- Click EDIT of the shipping method you want to edit
- Type and select the category / collection you want to exclude.
- Click SAVE