The number of complaints filed with the Federal Trade Commission (search) over Internet auctions has nearly doubled over the last two years, the agency said Tuesday.

More than 98,000 grievances about online auction transactions were filed with the FTC in 2004, up from 51,000 in 2002, according to the agency's annual report on consumer fraud and identity theft complaints.

The online auction concerns covered issues ranging from the failure of sellers to deliver their goods or services to the winning bidder to consumers claiming that their new purchase wasn't worth the money they paid.

The number of such auction sites has ballooned in recent years because these increasingly popular sites allow Americans to buy or sell goods from their home or office computer.

Overall, Internet auction-related complaints were 16 percent of the grand total of 635,000 grievances filed with the FTC in 2004, up from 13 percent from 2002, the report said.

The only other category in which more complaints were filed in 2004 was identity theft — 39 percent, or over 246,000 of the total complaints. It was the fifth straight year that identity theft topped the list of consumer concerns.

Identity theft (search) involves the stealing of someone's personal information for financial gain.

The most common cases of identity theft involved credit cards, followed by telephones or utilities, banks and workplace fraud.

The third most common complaint involved shop-at-home or catalog sales, accounting for 8 percent of grievances in 2004. It was followed by complaints about Internet-related service issues (6 percent), such as undisclosed Web site charges and spyware; and foreign money offers (6 percent).

The report did not include complaints involving the national do-not-call registry (search), in which Americans who want to be left alone by telemarketers can list their phone numbers with the government.