Pay per click search engines can be an effective way to drive qualified traffic to your web site. Much like an auction, pay per click search engines work by allowing competitors to "bid" for the highest position on search terms. These search terms are what people in the Internet marketing biz like to call keywords. They are the words people enter into a search engine to find a product or service.

Rates for keywords vary. Niche keywords that only a few people search for at any given time may only cost a few cents per click-through for a top position. Highly contested keywords however, may set you back several dollars every time somebody clicks on them.

For example, suppose you are an online retailer who sells "organic dog food." If you wanted to get top placement for your keywords in a pay per click search engine such as Yahoo SM, you would only have to bid around $0.11. Now if you are a travel agent, and your keyword is "discount airfares," you would have to pay considerably more for top placement. It is also important to remember that rates fluctuate over time, so while a bid of $0.76 might give you a #1 ranking in the off season, during peak travel months, when other travel sites are vying for search engine supremacy, you may have to bid substantially higher to keep ahead of the competition. For instance, if you are at #1 for $0.76 per click-through, than your competitor can knock you down to #2 by bidding $0.77

With most pay per click search engines, you only pay when someone clicks on your link in the search engine's results page. If you bid $0.76 for a keyword, each time a visitor clicks-through to your site, you pay $0.76. While that might not sound like much initially, over time it can add up, especially if your web site receives a sudden influx of visitors. Also, keep in mind that most engines specify a minimum amount of money to be paid before an account can be opened.

One argument against using pay per click search engines is that their results are not relevant. Many believe that allowing companies to bid for top placement will decrease the usefulness of search results by allowing any company with deep enough pockets to rank high for any keyword. But pay per click search engines know that irrelevant results will cost them searchers and eventually advertisers, and so make relevance a priority.

Many pay per click search engines have strict relevance guidelines and employ editors to review incoming requests for bidding. These editors are responsible for making sure that the submitted keywords relate to the web site's content.