Some people would like to use Google Adwords to bring traffic and to boost their sales. But I still think getting traffic from the natural means is the best quality traffic you can get. The key here is the content network.
If you really go for Adwords, for example you want to sell computer parts, you want your ads to appear on Cnet - not home shopping network. Also, you have to keep in mind your profit margins on the product/service you're selling. You may be able to sell a ton of pc parts, but if you are only breaking even, it doesn't make sense to continue on that path. While you may only find a few margin items, those are the ones to focus on first, so that you are generating revenue while determining the best strategy to go after new phrases. Your sells and success also depends upon the relevancy of traffic you are getting and the source from which you are getting it.
Adwords is the main key source of click fraud for PPC. But if you're not averse to taking a risk, content traffic will be cheaper. It all depends on your topic and your site. I have some sites that thrive because of content clicks while other areas they are just a waste of money... so it really depends on what type of site that you have.
It also depends on just how targeted the traffic is. You can find many top ranking websites still making thousands of dollars from Adsense and other contextual advertising because on some very hot websites, real buyers are searching for the products. While in some cases, even having a number one ranking may not help.
For example, If you are just visiting the GameSpot website and a nice ad grabs your attention about the XBox, you might even click and go further to discover, and might finally buy it even if some other websites selling this item is at no.1 rank in Google, but have you visited them? No, so highly targeted advertising in some cases can bring many new orders and customers.
Besides the click fraud on PPCs, do you believe that many people click the ads just for fun! This is not very helpful for you to bring sales in fact it is just wasting time and money. I would rather buy links on high trafficked sites which will definitely drive in a lot of traffic to my sites.