It’s an art of taking your customers to better and complementary products to whom they have shown their interest. By upselling you can make sure customer pick right product and they have everything they need to use product.
Well trained and knowledge agent can lead to boost in revenues by selling more products to same customer and alongside customer experience as well getting help in finding right product for their instant need.
If you are not suggesting relevant products, you are going to have poor through which ultimately not lead to enhance the customer purchase experience or your revenue. Making a live agent on upselling will give customer more comfort and knowledge of buying more products and increasing revenue.
Although your motives are always going to be increased sales and average order size, it's important to also consider the experience from a customer perspective and providing better experience.