In the ideal world, when you want to buy a product or a service, you would consider the value it brings to you based on hard facts, consider other circumstances impacting the costs - like e.g. product A is a bit better, but product B has support people in your country, speaking your language, etc.
Suddenly, comes product C. It's very much inferior compared to A and B, but the producers of C spent most of their budget on sales and marketing. Your boss knows all about C from on-line ads. A C salesman comes to you, promising you features they know they won't deliver, but also know they'll be able to weasel their way out of along the way. Oh, and he brings some nice "off-the books" benefits for you personally, as part of "building customer loyalty".
Sales and marketing as applied in practice distort the market. What a salesman says can be - and often is - completely disconnected from reality, so in presence of salesmen, products are no longer chosen based on objective value they provide. The incentive structure this creates makes everyone else have to lie too, or go out of business.
That's why many people don't like those skills and practices.