How Does a Price Comparison Site Work?

By Mary Simpson

Visiting a comparison shopping site helps buyers make informed decisions.
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Consumers use cost-comparison sites for two reasons: either to locate the lowest possible price on a specific item from a merchant with a good reputation, or to access information and reviews about a range of products in order to make a selection. Pricing is the focus of most current shopping engines, although some small start-up companies are specializing in presenting product information to help buyers choose the right product, according to the SmartMoney website. Even if the item is not purchased online, the consumer gains some perspective on whether the prices displayed in stores are good ones, factoring in what shipping costs might have been.

Why Cost-Comparison Sites Work

Briefly, they can save you time and money. Instead of going from store to store, hunting in the Yellow Pages or even bringing up individual merchant sites on a search engine, you can visit a comparison shopping site and view even more information than these other methods would have yielded in a matter of minutes. To save money is the primary reason most shoppers rely on the cost-comparison sites. The sites offer an alternative to buying the first product you see at the first price you see.

Crawling Merchant Sites

Comparison shopping engines obtain their information in one of two ways: by "crawling" or through "data feeds," the RoboShopper reports. The first method, crawling, employs a software program that visits and analyzes merchant websites to capture data and prices on the products they offer. Fewer shopping engines rely on crawling now. While this data-retrieval method works well for general search engines, merchant sites may not give the same product description or product title, so it becomes difficult to know if identical products are being compared by a shopping engine.

Data Feeds From Merchants

Most cost-comparison sites currently use the second method, data feeds, to acquire information. Merchants prepare these data files and make them available to the shopping engines. This is a faster and easier way for comparison sites to obtain their information, but they only receive the product data that the merchants want them to have. The merchants might focus exclusively on their most popular or profitable items and not include all their products, according to RoboShopper.

Shortcomings of Each Type

Some of the drawbacks have already been noted. Basically, crawling is difficult because of variances in how products are described or named on the individual merchant sites, because a format change on a merchant site might prevent the crawler from working properly, and because the crawler must constantly visit the same sites to ensure that information is up-to-date. On the other hand, data feeds are only as current as the merchant makes them, and as a result, the information on the cost-comparison site may not match what is displayed on the merchant's website.

Why Shopping Engines Give Different Results

Because of the problems with each method of information retrieval, price comparison is not an exact science. Using more than one shopping engine in your search is recommended by SmartMoney. Some engines focus on a specific category of products, like electronics. Others only feature listings from retail partners. The inclusion of shipping information and consumer product reviews may affect the value of one cost-comparison site as opposed to another.