Pay per click search engines have become the latest resource for online advertisers.

Their popularity is based on the ability of advertisers to spend money on advertising based on their sales revenue.

Advertisers can decide how much they can afford to spend per customer, and then limit the amount of advertising accordingly.

Similarly, an advertiser can increase his or her advertising budget according to the success of the pay per click campaign.

In lay men terms, a pay per click search engine is an advertising tool that allows the advertiser the ability to set his own rate.

The business model is based on allowing the advertiser to set his own spending rate based on his need for customers, and his ability to close sales on that traffic.

By introducing this advertising model search engines like Google, Overture, and now Yahoo, have been able to attract business from small and large advertisers.

A small comic book shop can decide to spend a hundred dollars a month on Google Ad Words, while an online giant like Amazon can spend millions of dollars per week.

Flexibility also makes the PPC medium work for advertisers. Modifications to their campaigns can be made in real time, and can be changed as market developments take place.

For instance, you can use your pay per click campaign to advertise a special sale, and then change your ads once the sale is over.

Or you can direct traffic to a specific page on your site that sells a currently hot item.

As an advertiser you select key words which will trigger your ads. When a search engine query is performed your ad will be shown as long as you selected the searched for term.

The search engines will match up ads based on the key words the advertisers want their ads to be shown for.

Caution must be used since words have alternate meanings to different people.

While pop might mean a certain sound or effect to you, it can also mean soda, or even surprise to another person.

So when you advertise using a pay per click search engine make sure that your ads are very clear. You only want people who are looking for what you offer to click on your ads.

The best way to avoid curiosity clickers is by making it very clear what the product or service being offered is.

This way a curiosity clicker will only visit your ad if he or she already has some interest in your business.

In the pay per click model you pay every time someone clicks on one of your ads, so it becomes crucial to attract serious prospects.

Donny Lowy has set up http://www.billionfreeads.com to show entrepreneurs how to advertise for free.