The Pew Internet & American Life Project's phone survey found that 17 percent of Internet-using adults have sold goods or services online, with about 2 percent selling something on any given day.
"I'd say these numbers were only moderately surprising," said Amanda Lenhart, the senior research specialist at Pew Internet who co-authored the survey. "It doesn't seem out of the ordinary, given the popularity of sites like eBay and Craigslist."
EBay and Craigslist are examples of the two most popular online methods Americans use to turn stuff into cash, said Lenhart: auction and classified advertisement sites.
"Twenty-four percent, or 35 million, have participated in an online auction, either buying or selling," said Lenhart. About 32 million, or 22 percent, have used online classifieds to sell things or for other activities, such as apartment hunting. "People are comfortable [with these sites]."
The demographics of online sellers are classic "early adopter," Lenhart added. Characteristics such as heavy Internet use, broadband access, and online experience mark sellers. Those who have been online six or more years, for example, are twice as likely to sell online compared to those who have used the Web for four to five years, and almost five times more likely than people online just two to three years.
The age group most likely to sell online is the 20 to 40 cohort, the so-called "GenX."
"People in their 30s are the ones who are doing this," said Lenhart. "They just have more stuff to sell, that's got a lot to do with it."
While eBay has the lion's share of the online auction market, the numerous sites under the Craigslist umbrella top the classified advertising charts, Lenhart said in her report, citing data from comScore Media Metrix.
"Craigslist had nearly 9 million unique visitors in September, 2005, but people are also using more specialized ad sites to sell and buy cars or even pets," said Lenhart. Cars.com, for instance, tracked third in Media Metrix's data, with 3.7 million unique visitors, while Puppydogweb.com came in seventh with almost 800,000 visitors.
Craigslist and other online classified ad aggregators may soon face competition from search giant Google, which launched a beta of http://base.google.com/base Google Base, the Mountain View, Calif.-based company's sortie into classified ad and other user-provided content. "The classified ad space is crowded, but that doesn't mean that there's not room for a brand like Google," Lenhart said.