First, my definition of buying traffic differs from PinUp-Net.
Placing ads, be it banners, video ads or any other kind of adverstising, is not buying traffic for me although it seems to be for @www_PinItUp_net. That's what Google Adwords is all about. I mention Google Adwords because it is, for sure, the biggest advertisement network that you can find.
The success of these ads varies for various reasons. Some of those reasons are under your control. Some are out of your control.
Writing or creating a good ad, that it is truthful but at the same time enganging and clear, is something that you could do.
Also, targeting the right group is something that you can control and this comes under understanding your customers and potential customers, their expectations, what they need, what they want... and what they want but they don't know they want it... yet.
These ads will be sent to the website of those persons who authorized the network company to publish that publicity. These people will create some frames to show these ads. And this is one of the things you can't control. You don't know where the ad will be placed or how good that guy will be at placing those frames.
You can be sure that he will want to earn as much from your publicity. After all, you're paying that unknown guy per each click (via the advertisement network)
This would be the equivalent to place an ad in a newspaper, or a radio station or even TV. Although today we call it Google Adsense, Facebook ads, etc.
Can you call that "buying traffic"? Well, it is buying traffic but I personally call it marketing campaign
Does it work? That depends on how good you are finding the right search terms and how good your ads are and where they are in the website where they're published.
Now, if someone offers you "thousands of clicks and traffic to your site, visitors from 45 countries in the world and blah blah blah..." I'd start running and wouldn't stop till I'm at the other side of the country.
It is very rare to find an honest company. They do exist but they're very rare. Most of the time, these companies (at least, the scammy ones) use scripts to simulate visitors. Sometimes you notice by their erractic browsing. And even if they're real, they're not interested in your products or your company. This means, this is not targeted traffic. They're paid to view ads while their browsing. It is rare that a non-targeted visitor wants to interact with your company and, at the end of the day, this is what is all about.
The results with this kind of traffic are very low.
Is it worth it? Again, with some honest company, if you have a terrific ad, honest, well explained and engaging, you may get results but the hard thing is to find that honest company and it is a lot effort.
You want targeted traffic because the chances that they buy from you are higher. At least, they're interested on what you have to offer