The sports apparel manufacturer will prohibit sales on those marketplaces.

Adidas Group will prohibit its dealers to sell its products via eBay.com and Amazon.com, says a spokesman for the German-based sports apparel manufacturer. The policy will be rolled out globally, though the spokesman gave no  timetable.

“We are regularly analyzing and differentiating our distribution channels,” the spokesman says. “Our new e-commerce guidelines will ensure that Adidas and Reebok will be presented in the right environment at all times.” He gave no further details about the reason for the change.

Adidas America Inc. is No. 212 in the Internet Retailer Top 500 Guide. Its Internet Retailer-estimated sales in 2011 were nearly $78 million. Amazon is No. 1. Requests for comment from Amazon and eBay were not immediately returned today.

“I don’t know the specifics of why Adidas is doing this, but we are seeing similar activities for a couple of reasons,” says Scot Wingo, CEO of e-commerce services provider ChannelAdvisor Corp., which helps retailers sell on such online marketplaces as Amazon and eBay

He gave two main reasons why retailers would withdraw from those online marketplaces:

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• The disruption caused by “showrooming,” which describes consumers using bricks-and-mortar stores to inspect products that shoppers will later buy online for lower prices. That can lead to pressure from offline retailers for manufacturers to have tighter control over what is sold online.

• Brand control. “A lot of brands do not want their prices to be different across different channels and they view this as one way to achieve that,” Wingo says.

Wingo pointed out one potential downside of a manufacturer stepping back from Amazon and eBay. “eBay has 100 million active buyers and Amazon has 173 million active buyers,” he says. “Can they really afford in today’s climate to not have their products in front of that many potential buyers?”

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