Great salespeople always try to increase the sales amount. This isn’t anything for a salesperson to feel guilty about. As a salesperson, that’s your job—as long as you’re honest.
Often, you can upsell or suggestively sell by identifying a customer’s fears. If you can understand what customers are worried about, you can demonstrate how additional products and/or services can genuinely help alleviate their problems. For example, “Have you ever gotten home, ready to paint and discovered you were out of masking tape? We have several types right here.”
Other times, you’re appealing to upsell a customers’ desires, which sometimes are not clarified in their own minds. If you can identify what a person is really after (e.g., not a specific car but a safe, affordable car that’s a little sporty) you can gear your selling toward meeting that desire which can often make a larger sale, as well as make the customer truly happy.