The advertisement posted on a fashion store on Weihai Road in Shanghai reads "Buying on your behalf from overseas." [Shanghai Daily]

University student Jessie Liu is a walking encyclopedia when it comes to purchasing low-cost foreign cosmetics on the Internet.

Well-known brands are much cheaper overseas and many Chinese women buy them online. Some buy them abroad when they travel, bring them home to sell and make a killing. Health products, nutritional supplements, fashion and accessories are popular.

Liu, a 20-year-old student from Shanghai University, has collected more than 400 Website addresses in her browser's "Favorites" folder, all for purchasing from overseas for herself.

But Liu has been on high alert since February when she discovered online that she might have been buying expired or fake products all along.

"It's just money," she says, "but I'm really worried about all the cosmetics I have bought and used. What would happen to my face if they are expired or fakes?"

Liu and her friends got worried after discovering a hot online post titled "Top Credit Online Stores Are Found Selling Fakes." At first she ignored it, saying "these kinds of rumors are posted online all the time, with no evidence to back them up."

But the anonymous post author explains the differences in details and posted comparative pictures of the genuine and fake packaged products.

The difference is often in the fine print, maybe just a letter, in the often-ignored bottom line of the content description.

The post generated a firestorm: More than 300 responses in 10 hours, 6,000 within a week, then up to 10,000 and still going.

The author also cites more than 30 popular online stores that allegedly sold fake or expired fancy cosmetics, including Taobao, a Chinese version of eBay.

All the stores are highly rated by buyers and sellers who post thousands of positive comments. Many have a satisfaction rate of 99 percent.

The author's claims have not been verified, but the concern appears to be timely.

After the posting appeared, generating an uproar, many online stores, including Taobao, asked sellers to remove cosmetics and medicine, two of the most sought-after products, pending investigation and verification.

Some cosmetics and health products have been restored to their online stores.

Fashion editor Momo Huang of online women's magazine, White Collars Fashion, cautions against buying cosmetics online.

"You should be careful about what you put on your face," she tells Shanghai Daily, "and it's difficult to verify that online cosmetics are genuine."

Many people who responded to the original posting reveal they have bought cosmetics from those online stores and never suspected a problem.

Like Liu, many were torn between denial and concerns about the products.

Some were furious - there was so much verbal violence from the ladies that the forum had to remove the comments.

Dai gou, which stands for "buying on someone else's behalf," is not new in China. In the 1980s, people asked friends or relatives going to Shanghai on business to bring back some fashionable accessories that were not available elsewhere.

In the 1990s, the destination became Hong Kong, as it became easier to go to the "shopping heaven," where prices for cosmetics, electronics and luxury brands are much cheaper.

As the Internet developed, people didn't need to ask travelers to shop on their behalf. Online shopping became popular.

Taobao has a special category for purchasing from overseas.

Website statistics show the revenue in this category rose to 520 million yuan (US$76.1 million) in the first quarter of 2008 from 9 million in the same period of 2007, an increase of 481 percent.

The global financial crisis has given a big boost to the online business since last June.