The Psychology of Giving Customers Free Delivery
This is hardly weird behavior; just look at your own habits to prove the point. You would pay a great deal for a great meal, but just think if the waiter was to ask you for a large tip directly. That tip money is only a fraction of the meal, but there is a chance that you would not pay it, or in a best case scenario, only do so very grudgingly.
Even though a purchase may seem to be a single transaction, customers often split up the different aspects of that purchase into a completely separate transactions in their heads. In the world of e-commerce, one of the easiest splits that occur in the heads of customers is the delivery charge, because it is so often separated as a line item in the receipt.
It is these extra little charges that people cannot stand, and that is why giving free delivery for online shipping is such an effective technique for closing sales. Also, because the delivery charge comes at the end of the transaction and is not included in the product purchase price, people can feel blindsided, especially if the shipping charge would have been quite a large percentage of the price of the product.
However, this is a psychology that you can actually use against itself. If people get to the last page of a purchase and they see that the delivery charge that would have been huge has been completely forgiven, they will walk with goodwill towards the entity that kept their feelings in mind so readily.
But to go back to the main point, you can still charge people for the delivery, and actually even make money on the delivery by simply including the delivery charge in the price of the product. If you sell the products well enough, the psychology of the seller will allow them to justify paying that extra money. if they are in a hurry, as they often are when they purchase online, the extra money will not even register, especially if they do not have a competitor's price to compare it against.