Your computer screen is aglow with a photo of the vintage Coach bucket bag, worn to perfection, that you’ve always dreamed of. And it’s being auctioned off for only $5 (a trope of seasoned eBay sellers, since the bargain draws lots of bids and bidding wars, which quickly drive up the price). How do you know if it’s too good to be true? To start, check the reputation of the dealer, says Jim Griffith, author of The Official eBay Bible, (www.amazon.com) (Gotham, $23). Look at the “seller information” box to the right of the product you’re looking at and check the “positive feedback” percentage. “A good seller’s rating should be 96 percent or better,” Griffith says. The seller should also have an eBay history — a 100 percent feedback rating doesn’t mean much if the person has been selling on eBay for only a week. As with any brick-and-mortar company, happy customers make for repeat customers. How can you tell? In the “seller information” box, click on the “read feedback comments” link and compare the number under “members who left a positive” (say, 498) with the one under “all positive feedback received” (say, 779). The larger second number means 281 are repeat customers.

Once you’ve OK’d the seller, parse the description. Count out anything with vague wording, no photos, faraway photos, or blurry photos. The seller with a real Marc Jacobs purse, for example, should say specifically that it’s “authentic,” may include the dust cover the bag came in, and may feature a close-up photo of the bag’s label, stitching, and hardware. (Also, if there’s a defect or a stain mentioned in the text, there should be a photo of that too.) Take advantage of the “contact member” link and ask the seller specific questions: “Is it authentic?” “Can you send me more photos?” One final safety net, suggests Griffith, is to buy only from dealers who accept PayPal, which allows you to file a claim if you’re not satisfied with the product within 45 days of payment. “It protects you as a buyer for purchases up to $1,000, and a bad seller can face sanctions,” Griffith says. “If he wants to keep selling on eBay, he has an extra incentive to keep you happy.”