SAN FRANCISCO A brewing conflict between Amazon.com Inc (AMZN.O) and its merchants over fee hikes could benefit rival eBay Inc (EBAY.O), and provide an opening for Wal-Mart Stores Inc (WMT.N) and Google Inc (GOOG.O), which are just getting into the space.
Amazon's online bazaar generates margins many times higher than traditional retail as the company takes a cut of every sale on its site made by a merchant, known as a third-party seller, and charges extra fees for handling logistics.
The growth of this business, which now accounts for almost 40 percent of unit sales, has helped push Amazon shares to record highs.
But a series of fee hikes over the past year and a half have alienated many merchants, and some are threatening to defect.
"If they increase fees too much, some sellers will decide to not sell there anymore," said Niraj Shah, chief executive of furniture retailer Wayfair, which uses Amazon, eBay and Wal-Mart's online marketplaces, as well as its own websites.
"That's against Amazon's plan, which is to get as much selection as possible on their site," Shah added. "The vast majority of Amazon sellers are perfectly happy to go to any marketplace offering meaningful volume."
Amazon said many of the fee increases have been driven by rising costs, such as higher gas prices and hence transport expenses. It said it has also invested in changes to get products to customers quicker - a push that third-party sellers will benefit from because faster shipping should increase sales.
But sellers see it differently, complaining on online seller forums that Amazon's fatter returns came partly from putting a heavier burden on their shoulders. "Shipping & fees are killing my margins," wrote one seller last month.
Another, in August, complained about higher fees for selling electronic accessories that were due to kick in early this year: "Holy crap! 8% to 15%?! Goodbye good deals from 3rd party sellers on Amazon in the electronics section."
A third ranted in August about higher costs for shipping products to multiple Amazon warehouses. "Amazon just pulled a fast one," the seller wrote. "Now that Amazon has all the power, they're imposing increased fee hikes to all those cozy sellers who have supported Amazon since Day 1."
The complaints became so raucous last year that the company took the forums down and re-launched them. The new forums let sellers give each other ratings for their posts - a move that some sellers viewed as a way to reduce extreme complaints.
"The updated forums were created to be more responsive to the needs of the seller community and give them information they need to help build their businesses," Amazon spokesman Erik Fairleigh said.
EBay used to be the top online destination for sellers, but Amazon's marketplace ended its reign after its launch over a decade ago, helped in large part by "Fulfillment By Amazon," or FBA, a service that stores and ships items and even handles customer service on behalf of sellers.
Fees are a touchy topic for sellers with skimpy margins, as eBay knows from merchant revolts it has struggled to quell in the past. Fee hikes by Amazon are particularly irksome to sellers because they compete with the company, a seller in its own right, in many categories on the site. EBay does not hawk its own wares.
When Amazon introduced a new long-term storage fee for items that sit in its warehouses more than a year, some sellers elected to have the company destroy their unsold inventory as it was cheaper than getting the items shipped back to them.
Kat Simpson, a third-party merchant who also trains others how to sell on Amazon, said the company charges her 50 cents per item to return unsold inventory from its warehouses but just 15 cents per item to destroy it, she said.
"I would have said everybody needed to try FBA last year. Now I would say no," she said. "If you are selling items under $25, you won't do as well on Amazon as on eBay profit wise."
It costs $3.92 to sell a $10 item on Amazon and $2.72 on eBay, according to Bill Vogel of The Cumberland Companies, which sells on both. But eBay takes more time and most merchants store inventory themselves, adding other costs, he noted.
For now, many merchants remain tied to Amazon's marketplace, which has two million third-party sellers.
"Customers like lower prices, but customers also like greater convenience, faster shipping and great selection," said Tom Taylor, vice president of Amazon's FBA business.
Some seller fees, particularly for some larger products, have been cut, he noted.
Wal-Mart's marketplace now features just six merchants: Wayfair, Plumstruck, eBags, ProTeam, ToolKing and Shoebuy. Spokesman Dan Toporek said the world's largest retailer is trying to expand available products and it "is a key component of that strategy to accelerate the growth."
Google may be the bigger threat. It already owns most of the necessary pieces, such as product search, listings and a payment service -- it just hasn't combined them yet.
It began testing a same-day delivery service with retailers in recent weeks, sparking speculation it's building a marketplace. A spokeswoman said Google is always working to improve the user experience, including shopping.
"If somebody comes in, a Google for instance, and says you can list with us and we will give you wide exposure at much lower cost, that would be a problem for Amazon," said Scott Tilghman, an analyst at B. Riley Caris.
Consumers want selection, bargains and fast shipping, which all cost money. Getting sellers to cover those expenses could drive them elsewhere. Yet if marketplace operators cover such costs, their profits suffer and shareholders grumble.
"There's always a trade-off," said Ken Sena, an analyst at Evercore Partners. "There's always that risk that sellers could defect."
(Reporting By Alistair Barr; Editing by Tiffany Wu)