As more and more shoppers go online, the chances are slim that any one potential customer even knows your web address, much less wants to shop specifically at your site. However, ecommerce retailers can reach out beyond their websites and connect directly with shoppers through product comparison services. These product search engines are the yellow pages of the Internet, where customers look up products and find your directory listing, as well as the prices you offer and a wide range of comparable products from your competitors. This is a great way to add your products to the search results of consumers browsing for the things you sell. These gateway sites, from Google Product Search to Shopzilla.com, do not sell products directly, but they list products that link to ecommerce sites.

There are many product comparison sites out there, and some are better than others. Merchants looking for places to push their products would do well to focus on the best of the bunch. Two years ago, The Wall Street Journal surveyed and rated nine of these sites. In October 2010, Consumer Reports looked at 25 product comparison sites. The top portal on these lists, both then and now, was PriceGrabber.com, the product search engine that also powers Yahoo! Shopping, and until recently, Microsoft Shopping Network. MSN has now shifted over to the new Bing Shopping. AOL Shopping has used PriceGrabber.com in the past, but now coyly says its shopping results are powered by a "third party." Consumer Reports puts PriceGrabber.com at the top of its list and cites Google Product Search, NexTag.com, and Bing Shopping as runners-up. The consumer watchdog organization also called Shopping.com and Pronto.com the "worst," so merchants may want to steer clear of those.

CPCStrategy.com, a data feed management company founded by people who used to work for PriceGrabber, evaluates these kinds of sites quarterly. CPC's most recent ranking lists the top ten companies as: Google Product Search, Amazon Product Ads, Shopping.com, NexTag, Shopzilla, PriceGrabber, Bing Shopping, Become.com, TheFind.com, and Pronto.com. CPC says that the right comparison shopping engine strategy can boost revenue by five to ten percent. Most of these sites require retailers to set up an account and pay real money whenever a shopper clicks on a listing and is linked to a product result page on the retailer's website. These sites generally only charge for these clicks, or leads, as the jargon goes. The cost per click can be as low as a few cents and rise to over a dollar, so for retailers selling very low priced goods, the cost of a few leads may eat up all the profit on the item. However, the good news for budget conscious online retailers is that some of the best sites out there are also free.

However, PriceGrabber.com, Consumer Reports' top rated site, follows the price per click model. On its website, the company touts itself aggressively, saying, "PriceGrabber attracts over 24 million unique visitors each month, and provides the easiest and most comprehensive environment to find and select the right products and shop." Still, since The Wall Street Journal and Consumer Reports both seem to agree, it might be worth paying per click to get involved. The company details its pricing structure for a wide range of product categories: for example, ranging from $0.35 per click for auto parts, up to $1.15 per click for computer printers and televisions.

Two runners-up, however, are available at no cost to merchants, and Google Product Search, formerly called "Froogle," tops that list. Google offers retailers increased traffic and sales to qualified shoppers for free. The company makes money by putting its AdWords product ads around and into the search results. Retailers can add products to the search engine by submitting data feeds, direct uploads, or for the tech-savvy, through Google Product Search's API (Application Programming Interface).

Bing Shopping, part of Microsoft's relatively new Bing search engine, is very much like Google Product Search. It is a little less user friendly, however, because it requires merchants to set up a Microsoft AdCenter account and to put a valid credit card on record. The company says that it will not charge the credit card if the merchant sticks to Bing Shopping only. Bing's data submission requirements are also fairly strict. NexTag is another pay per click site that is highly ranked by both The Wall Street Journal and Consumer Reports. In fact, it is one of Consumer Reports' three runners-up, along with Google and Bing. Of the remaining major price comparison websites, it is the most highly trafficked, with an Alexa ranking of 240 in the United States, compared with 453 for TheFind.com, 570 for Shopzilla, and 598 for Shopping.com. Lower numbers are better for Alexa rankings. NexTag charges a little less per click, about $0.10 below PriceGrabber.

Two more free product comparison sites may be worth a retailer's time. TheFind is free, offers good web traffic, and specializes in mobile shopping and social media integration via Facebook. ShopWiki is also free, and since it uses Internet robots to crawl retailer websites, many retailers are already listed there without even knowing about it. Both sites offer programs that encourage retailers to work more closely with the product search engines. Two other pay per click sites to consider are Shopzilla, which feeds results into the BizRate and AOL shopping engines, and Become.com, which has recently focused on keyword results.

According to CPC's Chris Dawson, it takes a comprehensive strategy to really excel. He advises online retailers to really dig deep into the ins and outs of how comparison sites work. He advises retailers to devote the resources needed, and suggests that retailers need a bidding strategy and the right data feed to succeed.

The Consumer Reports feature advises shoppers to visit multiple sites, look for specific product information, and click-through to make sure search engine results are accurate. When it comes to product comparison websites, the magazine tells consumers, "The best ones make it superfast and easy to dig up juicy bargains; on the other hand, the worst ones can be real time wasters." That advice applies to online retailers. Make sure you are offering those juicy bargains on the good sites, and stay away from the ones that waste your time and resources.