I often encounter many such salesmen. They start by saying how good our company's products are, and then how bad other companies' products are. Our products far exceed those of a certain company in this and that aspect... etc. Whenever I hear such rhetoric, my first impulse is to leave; I simply don't have the courage to continue the conversation!
This is because they have made a very fatal mistake: belittling others to elevate themselves! Is it effective? No, it only makes people dislike them. Because no customer is a fool! Don't expect him to believe only what you say!