Acknowledging that caveat emptor goes only so far as a guideline for online sales, eBay has been putting new mechanisms in place to help fight fraud.

We want to know what your experiences have been as a buyer or seller at the auction giant. Have you bought something that turned out to be not what was promised? As a seller, do you think eBay is doing enough to protect your reputation?

We'd like you to post your stories, and any advice you have for buyers and sellers, to our TalkBack section at the end of this article. Then, in the near future, we'll summarize the replies and give a recap in another News.com story.

Last week, eBay highlighted some of its recent "trust and safety" efforts, prompted by what it says are the growing number, and increasing sophistication, of online criminals who target eBay and its PayPal online-payment service.

"Where we've historically put an emphasis on transparency and free choice, today, the security threats are more complex, and we're more actively protecting our buyers from fraud, as well as other bad experiences on eBay," Bill Cobb, president of eBay's North America marketplaces, wrote in a posting to the company's Web site that highlighted the company's priorities for 2007.

One area of focus is counterfeit goods. In addition to its earlier work with copyright and trademark holders, eBay is now taking several other steps for some sale items that are known to be favored by counterfeiters. The company is requiring additional seller verification for those items, which it did not name. It has eliminated the ability to list those items in one- or three-day auctions, and it has also imposed restrictions on selling them cross-border.

Even a small percentage of fake wares could be a big problem for eBay, which says it has 105 million items listed at any given time.

Other new programs have come under the heading of Safeguarding Member IDs, designed to protect those bidding on high-end items from fake offers and other malicious e-mail, and Buyer Protection, intended to ensure safe payments.

"So far," Cobb wrote, "these efforts appear to be paying off with minimal disruption to our legitimate sellers."

Along with protecting against fraud, Cobb said, eBay's high-level priorities for this year include simplifying the site so that it's easier to find things and holding sellers to higher minimum standards.

"It's clear we have a shared responsibility with our sellers to make sure our buyers have satisfactory experiences," he wrote.