In the first half of 2006, companies spent $2.5 billion to reach consumers online, according to a PricewaterhouseCoopers and Interactive Advertising Bureau report. But, to paraphrase advertising legend John Wanamaker, how much of that expense really works? Online, it's sometimes easier to know, especially when it comes to paying for clicks on search results. Google, Yahoo, and other search engines offer advertising programs that highlight your business when customers search for your related product -- and you only pay when someone clicks on your company's ad.

“The biggest advantage lies in your ability to manage your costs and spend strategically through only appearing for people who are making search inquires,” says Garrett French, a search specialist at Market Smart Interactive, a Morrisville, N.C. Internet marketing firm. “Every small business should experiment with paid search if they have an existing website that generates leads or sells product.”

Here are ways to make it pay off.

TIP #1: Consider the short-term and long-term benefits

Click-through ads should not only be looked at as a short-term sales opportunity, but as part of the company’s long-term brand awareness strategy. “Search engines act as brand builders as well as shopping tour guides,” says Catherine Seda, author of Search Engine Advertising: Buying Your Way to the Top to Increase Sales. “It’s interesting to note that search engine listings fall behind only print ads as a brand-building tool used by U.S. companies.”

TIP #2: Know the different search engines

Determine what your needs are and find what services match them best.

Google AdWords is the most popular click-through service. Google provides a link to your website and a short text ad every time a potential customer does a relevant search. It has partnerships with America Online, Ask Jeeves, and Earthlink.

Yahoo Search Marketing uses a system similar to Google. A key difference is the Content Match program: Yahoo takes traditional click-through ads and places them beside actual articles, not just related searches. Aside from Yahoo news content, Content Match includes articles from MSN, CNN, The Wall Street Journal and National Geographic..

TIP #3: Find out which search terms consumers use

Text-based click-through ads are like classifieds: the more words, the more it costs. Choosing the right words to “trigger” your ad are essential. “Any companies new to paid search should spend time doing keyword research to determine appropriate terms for bidding on,” French says.

He recommends using search engine software to find out what words customers usually use to find your site. Google, Yahoo, and other search engines can show how viewers reach you. Basic Web counter software can also give search information.

TIP #4: It costs whether they buy or not

Search engines charge based on how many people click through the ad -- not how many people are actually buying product. Experts recommend evaluating the cost of Internet ads without assuming every ad participant will buy. Also, be wary of “click fraud,” a growing category of crime in which competitors or organized rings of thieves click on your ad to drive up your costs.