It’s annoying. And it drives customers away.
Upselling and cross-selling are useful only if they are done with the customer’s interests in mind. If you get to know your customer and you understand what they want then making suggestions is often the best way to help them. That’s a natural part of good customer service.
Doing things this way can increase revenue. Even better, you create more customer loyalty because you help your customers get what THEY want (not what YOU want to sell them).
As a customer which do you prefer? Do you like getting product pitches that you have no interest in? Or do you prefer intelligent, thoughtful suggestions based on what you want? What do you think YOUR customers prefer?