Are these genuine designer bags or fakes? Consumer Reports offers tips for spotting counterfeit products, which the magazine considers to be an increasingly pervasive problem.

Whether it’s adulterated medicine that can kill, bogus batteries that can burn or wannabe Guccis that simply wear out fast (though they may look stylish for a while), counterfeit merchandise is almost impossible to avoid.

According to a recent investigation by Consumer Reports, 14,000 shipments of counterfeits were confiscated in 2006, a record year for seizures. Figures for 2007 were also high. And today’s fakes are not just the usual knockoffs, which means consumers need to take special precautions when shopping.

Every product is vulnerable, and fakes include truly unsafe merchandise. Investigators have seized brake pads made of kitty litter, sawdust and dried grass; power strips, extension cords and smoke alarms with phony Underwriters Laboratories (UL) marks; medical test kits that give faulty readings; toothpaste made with a chemical found in antifreeze; and cell-phone batteries that could explode. Online drugstores claiming to operate from Canada but actually based in other countries have peddled “Lipitor” and “Celebrex” pills stored under uncontrolled conditions and containing the wrong active ingredients.

Among the phonies are some typical suspects: handbags, clothes, watches and amusingly renamed colognes such as Essey Miyami instead of Issey Miyake. But there are also surprising fakes, including golf balls, oil filters and baby formula. With some, the low price is a giveaway, such as a $2,000 Prada purse for $35. Others are priced close to retail to fool shoppers.

Vendors still peddle fakes on city streets, flea markets, salons, swap meets, college campuses, libraries and “purse parties” in private homes, at which a dealer shows merchandise.

And counterfeiting is not a victimless crime. People selling $20 purses are fronting for crime networks that promote child and sweatshop labor, prostitution, human trafficking and gang violence, among other illicit activities.

The easiest way to avoid counterfeits is to deal with reputable retailers authorized to sell a manufacturer’s products. Be suspicious of third-party Web sites that offer deep discounts for products that are usually pricey. The auction site eBay said it has been the target of lawsuits and threatened lawsuits from the likes of Rolex, Louis Vuitton and Christian Dior for, in part, not doing enough to banish fakes. Manufacturer sites typically include a list of authorized resellers.

Here are some other tips:

¢ Think twice before buying at deep-discount and dollar stores, which have sold fake holiday lights, extension cords, toothpaste and batteries.

¢ Avoid no-name products. A manufacturer’s name and address lets people contact the company to try to remedy problems.

¢ Don’t buy if the seller won’t provide a receipt or if warranty data is missing.

¢ Missing or expired “use by” dates, broken or missing safety seals, misspellings or unfamiliar or flimsy packaging for big-name brands should send up a warning flag.

¢ For electrical goods, look for the UL safety mark. A silver holographic seal is required on decorative lighting made worldwide and on fans, other lighting and similar products made in China. Consumer Reports advises consumers who suspect a phony label to contact UL at www.ul.com.

¢ It’s especially hard to tell whether car parts are authentic. Use a mechanic who has been reliable or a new one who has been recommended.

¢ Shoppers who suspect that they purchased a counterfeit product should contact the manufacturer. Many company Web sites have a link for reporting suspected fakes. Some sites, such as Callaway Golf, spell out exactly how to spot knockoffs.