eBay's position angered Peter Togel, a South Carolina art gallery owner, who has sold on the site since 1999. He plans to quit selling on eBay altogether and move to a specialty art auction site that plans to accept Google Checkout.

"I was not been happy with eBay and PayPal for a long time,'' he says in an interview. "You can see from the changes on their Web site a direct negative impact on sales. I am not surprised sellers are frustrated.''

Even merchants who aren't angry with eBay may wind up using Google Checkout anyway.

Online merchants are increasingly offering more than one type of payment service to consumers. Offering only one is analogous to a bricks-and-motor store only accepting cash, says Marwan Forzley of Moda Solutions, a provider of payments services.

eBay, which has recently signed an alliance with Yahoo! ( YHOO), remains dependent on Google to drive traffic to its site. Google also is reluctant to publicly anger eBay, which has been one of its largest advertisers for years.

Shares of eBay already have taken a beating this year, tumbling almost 40% because of concerns about Google's competition with PayPal. PayPal head Jeff Jordan's decision to leave the company for personal reasons only added to Wall Street's concerns.

The shares fell 6 cents to $26.79.

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