Sidney,
It is like anything else in life. Those that are dissatisfied are the ones that are going to complain and those that are happy are more of silent majority.
That said, I have had some great salespeople that were knowledgable, helpful and took the time to listen to what I was shopping for and point me to one of their products that would meet those expectations. When I get one of those salespeople, I ask for some business cards, and I make sure to pass them to friends and family that are in need of their products with a glowing recc.
I have also had salesmen that clearly I knew more about their products from doing 5-6 hours of research on the internet and the manufactures website than they did. I one time had one argue with me, tell me I was wrong about the R factor of the insulation he was quoting on a fifth wheel until I made him go back outside and showed him on a sticker on the trailer that there was not as high a R value as he said in the floors.
So the sales person that is knowledgable and helpful in determining the differences on a major purchase (for most people) will always be successful and highly regarded. The "salesmam" that knows more about tactics, pressure, closing the deal than he does about the product he/she is selling, is going to be regarded like the the saying goes, "Their lying if their mouth is moving."