The appraisals, which will cost sellers $20 each, will be conducted online by Eppraisals' experts.
"Yahoo's feeling is this helps lend credibility to their site," said Eppraisals chairwoman Leslie Hindman. "This helps give their clients another option."
As online auctions have grown in popularity, a growing number of companies have cropped up offering sites and services to meet the needs of buyers and sellers. In addition to appraisal services, companies such as Bidder's Edge, X.com's PayPal and i-Escrow offer everything from auction search engines to person-to-person payment and online escrow services.
The deal between Yahoo and Eppraisals comes some seven months after AuctionWatch launched a similar appraisal service on its Web site. AuctionWatch, which drew a team of appraisers from eBay-owned Butterfields, charges $19.95 for its appraisal service.
But Hindman said Eppraisals draws on hundreds of more experts than AuctionWatch, enabling the company to provide specialists in particular areas of art, collectibles and other auction categories.
Eppraisals' service will be targeted at Yahoo sellers. While filling out an online form to list an item in Yahoo's auctions, sellers will have the option to ask for an online appraisal of their item. Sellers who have previously received an appraisal can link their auction to it.
Like those of AuctionWatch, Eppraisals' experts evaluate items based on descriptions and digital photos submitted by sellers. Neither service guarantees the appraisals.
Although Eppraisals experts will not physically inspect items, Hindman played down the possibility that an unscrupulous seller might try to use the service to defraud bidders.
"There's no real advantage to doing that," Hindman said. "If people have an intention to do something like that, they will do it online or offline."
Online auction leader eBay promotes a variety of authentication and appraisal services on its site, including the International Society of Appraisers and the Professional Coin Grading Service. Unlike the AuctionWatch and Eppraisals services, many of the eBay-affiliated services require an in-person inspection of the item.