In the fast and furious world of online auctions, it_s buyer beware.

Online auctions let you window-shop 24 hours a day, seven days a week, until you find what you want, without wearing out your feet or car. But be aware of the caveats before you start clicking on that bid box. Gomez Advisors in Lincoln, Mass., is a research company that reviews, ranks and rates e-commerce sites using more than 100 criteria, from ease of use and customer confidence to on-site resources and relationship services. "Don_t jump in and buy on impulse," said Hank Hudepohl, an analyst at Gomez. "People can easily get caught up in the fun or competition. It_s almost like gambling."He recommended researching a site and previewing the merchandise. Watch bidding and see how it goes. Read up on the rules, which differ from site to site. Most require bidders to be over 18. And, "If something seems too good to be true, it is." If you are very interested in buying an item, check the bidding action every hour or so. At eBay.com, for instance, potential buyers offer as many as 600 bids per minute. The site is the leading person-to-person on-line trading community, with more than 1,600 categories and more than 1.5 billion page visits per month. Although some on-line auction houses monitor their sites for strange bidding behavior and unusual listings, the buyer should still be cautious and savvy before starting to bid, according to on-line auction specialists. Some sites let you retract your bid if you accidentally hit the wrong key or change your mind in a certain time span, while others allow retracted bids until the last minute of the auction, Hudepohl said. On-line auction sites involve either business-to-consumer trading, as with Onsale.com, or consumer-to-consumer, such as eBay and Yahoo.com. Sellers register with an on-line auction site of their choice that caters to the type of inventory or item they plan to sell. They then select how many days the item will be for sale, which can be anywhere from three days to one month.