On a certain level, salespeople tend to bother me a little. Not so much personally - although one of the people at my undergraduate alma mater I found the most reasons to personally dislike ended up working as a car salesman for a little while - as in terms of the general concept of the role. The line between salesperson and scam artist can be very slim, and it's difficult to see, sometimes, just what they add.
There are two elements that combine to make salespeople hazardous. One is working on commission; the other is informational imbalance. If you work in sales, you probably are paid on commission, even if you work as a middleman between two parties (as, say, real estate agents do) rather than working directly for some manufacturer.
I can think of several scams that involve trying to hook lots of amateur sales-interested folk by requiring them to buy expensive samples or the merchandise they will sell, and then doling out a narrow commission. I say "scam" because some of these operations make their real money selling sample kits to would-be salespersons rather than moving merchandise through those salespersons. The commission is a powerful motivating tool.
Now, when combined with the information gap, a salesperson on the ground has every reason to outright lie to uninformed customers if it will get them to purchase something marginally more expensive, to incrementally stretch bit by bit their intended budget, and since little of it is written down, there's often little recourse for a consumer who has been deceived with a personal sales pitch.
I've been lied to by sales folk more than once myself. And by and large, the consumer is in something of a bind: They need an expert on computers, cell phones, etc that they can talk to, who will explain all the features they don't quite understand - but while the salesperson is such an expert, and a remarkably easy to find one, there's every reason not to trust them.
Oddly, my experience is that when there's no commission in play and a generous returns policy, employees working for a wage are perfectly willing to dish out honestly about which products do what and what you probably need for what you want to do. Remember all the jokes about used car dealers? The grain of truth in them is why I so tend to distrust salespeople. It's nothing personal, salesfolk; it's simply that I'm pretty sure your interests and my interests are as close to orthogonal as they could be given that we're talking about the same kind of product.