Managing a pay per click (PPC) campaign is quite hard. Sometimes it could be unpredictable. There are times when competition for a particular keyword gets too tough. Prices could inflate swiftly. As a marketer, you have to find ways to compete closely. But instead of becoming an achiever, some individuals waste their money by committing one grave mistake...

Here's one good material I found on the net.

Bill Hartzer writes:

As someone who manages many Pay Per Click campaigns through the Google AdWords and Yahoo! Search Marketing (and has been doing so for several years now), I often come across some pretty outrageous and costly Pay Per click mistakes. I recently uncovered a simple mistake that is costing companies thousands of dollars. This is my all-time favorite Pay Per Click mistake:

If you aren't in the Keyword business, then don't bid on the word "keyword."

Yes, there are many companies that venture in keyword research services involving selling "keywords" and keyword phrases." But these companies are offering PPC keywords that are related to their clients' business or campaigns. But there are companies which are bidding on the word "keywords" that are least linked to it. This mistake is repulsive and would just cost businesses their money.