While some people who shop on Amazon are only looking for items sold — or at least fulfilled — by Amazon, lots of you are also buying things from the many, many third-party sellers who use the site as an online storefront. And these sellers are getting increasingly savvy about having a price that will position their item in a space ideal for bargain-hunting shoppers.

The Wall Street Journal and Decide.com teamed up to look at pricing variations on items available at a variety of online retailers. Perhaps not surprisingly, Amazon showed the widest range of prices — and highest number of price changes — in a single day.

For instance, the price on one GE microwave changed nine times during the course of a single day, with the lowest available price ranging anywhere from $744 to $871 in that time.

Of interest is that when the Amazon high price spiked, the same item on BestBuy.com suddenly jumped from $809 to $899, where it remained until after the Amazon sellers’ prices dropped back to around $750. At that point, Best Buy’s returned to its earlier level.

Meanwhile, the price on Sears.com remained fixed the entire day at $899. Hey, at least Sears has a website.

More from the Journal story:

Last month, retailers on Amazon.com changed prices on a Samsung 43-inch plasma television four times over the course of a day, between $398 and $424, according to Decide.com. Around midday, Best Buy boosted the price to $500 from $400 before dropping it back down, while electronics retailer Newegg in the morning raised its price to $600 from $500.

These sort of rapid, follow-the-leader price changes are something that frequent travelers have long been accustomed to. And some online sellers are turning to similar algorithms used by the travel industry to figure out when they should raise or lower prices.

Brooklyn-based kids’ clothing retailer Cookie’s sells through Amazon and tells the Journal that its software checks competitors’ prices every 15 minutes to insure that its items maintain the coveted position either directly under the product’s name or under the “add to cart” button.

Mercent, the company behind this software claims that, between all of its clients, two million prices are changed every hour based on its algorithm, which factors in everything from competitors’ prices, to competitors’ shipping prices, to seasonal sales.

“The long-term implication is that a price is no longer a price,” said Mercent’s CEO.

This could be good or bad for consumers, if online retailers choose to compete against each other by keeping their prices low. However, only a small number of sellers will be willing to go the bottom-dollar route. So once that low-price stock is gone, buyers could be left at the mercy of higher-priced retailers.

Decide.com says it found that price changes appear to be split evenly between increases and decreases, so it’s up to buyers to pay attention to fluctuations and buy when they feel the price is right.

If anyone out there has developed your own personal system for tracking price changes at online retailers, share your story with us at tips@consumerist.com.

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