I've dealt with a fair number of salespeople in my time. Some of them come across as being high-pressure and manipulative, while others come across as being reasonable and helpful. What differentiates the two?

The question matters, I think, even if you don't happen to work in a company sales department or in retail, because all of us are salespeople at certain points in our lives. When was your last job interview? How well did you sell yourself? And even if you can't bring yourself to admit that you do have to play the role of the seller from time to time in your life, I always tell people they should read a sales book at least as a means of self-defense.

I'm also not talking about the times you walk into a store when you intend to buy something, you buy it, and leave. In that case, the salesperson hasn't really done anything; as far as you're concerned, they're just the human equivalent of one of those self-checkout machines they have in grocery stores. But there have been times when I've gone into a store and spent more money than I expected. And it was because the salesperson closed me on spending more. And I left a satisfied and happy customer.

But there have also been times when some salesperson tried to coerce me into buying something I really didn't want or need. (The warranties the clerks are peddling on commission at Best Buy come to mind.) This is just plain annoying. But what is the difference?

It's not in the tactics. Truth be told, in my experience with salespeople, there's been a lot of overlap of closing techniques between helpful salespeople and annoying ones. One example: the "alternate of choice" close...let the buyer choose between something and something, not something and nothing. ("Did you want to wear that lovely fur coat out or should I wrap it for you...?")

But when do these kinds of shenanigans cross a line? When do they start to bother us as shoppers? Pressure is pressure, after all, but on its own, pressure isn't always a bad thing. So what is it that separates the good from the bad?

Here's the key: salespeople come across as high-pressure, and not helpful, when they try to close the sale before they've demonstrated the value of what they're selling. If you manage to convince someone that the purchase will actually help them (note: I'm not talking about lying or being deceitful here), then you're okay to start gently nudging the person in the direction you want.

You can firmly and politely ask for a raise, but you'd better be sure your boss already thinks you're worth it.