Jonathan Garriss, executive director of the Professional eBay Sellers Alliance and head of Gotham City Online, which sells shoes on eBay, said his group's members are seeing fewer of their listed items sell, and lower average prices for things that do sell.
EBay has been rejigging its vast Internet marketplace in hopes of turning around a troubling trend: Its number of active users is barely rising. In the most recent quarter, the figure rose 1.4 percent to 84.5 million.
One big change came in January, when eBay altered its complex fee structure and said it was trying to encourage sellers to offer more items for sale, which in turn could attract more buyers.
Generally, eBay cut the fees it charges for listing an item, but raised its commissions on completed sales of products auctioned for less than $1,000 or sold at fixed prices lower than $100.
Meanwhile, the company began taking a lesser bite out of higher-end fixed-price sales - as much as 4 percent instead of a previous maximum of 5 percent.
At the time, eBay said more than 60 percent of its sellers would save money under the new rules. But plenty of complaints poured in.
EBay responded by cutting listing fees by as much as half for items in its "media" category - such as books and DVDs - that sell for under $25.
Still, many sellers were still unhappy that unlike in the past - when eBay consistently talked of a level playing field for brand-name companies and weekend attic-raiders alike - a new top tier of vendors seems to have an easier time flooding the marketplace.
Under a new "Diamond PowerSeller" plan, the highest-volume merchants may be eligible for reduced fees. One Diamond PowerSeller, Buy.com Inc., is offering so many goods on eBay that many sellers suspect Buy.com is listing items practically for free.
EBay won't comment on Buy.com's arrangement.
Buy.com's listings also emphasize eBay's move toward sales with set prices rather than its traditional auction format. EBay says auctions are not going away, but fixed-price sales are the fastest-growing part of the company's marketplace, increasing 60 percent a year.
And more changes are afoot. EBay announced Wednesday that starting Sept. 16, it will let U.S. sellers pay 35 cents to list an unlimited number of identical items at a set price, for a month at a time. Previously, fixed-price listing fees could run as high as $4 per item, and the listings were good for a week.
EBay also plans to move nearly all transactions to electronic payment methods. Beginning in the U.S. in mid-October, users will have to pay by credit card, PayPal or the credit card processing service ProPay. No more cash, checks or money orders - which account for less than 10 percent of eBay transactions these days - unless sellers and buyers meet in person.
EBay's president of marketplace operations, Lorrie Norrington, acknowledged there has been "a lot of change" this year. But she said the company carefully considered the moves and believes they are improving buyers' experience because "the best values from trusted sellers become better and better."
For some sellers, like Michael Knight, who dismantles motorcycles and sells the parts on eBay from Garland, Texas, the sheer volume of recent adjustments has been frustrating.
"I have no control. I have to comply with anything they choose to do and I have no voice in the matter," he said.
Knight would like to move off eBay, but says it's difficult to transfer his listings to another site. Other sites will not easily accept the photos embedded in his item descriptions, and modifying every one of his almost 4,000 listings "is just not practical."
"I'd be giving up a month's income to get that done. That's the only thing that's keeping me on eBay - the inconvenience of leaving," he said.
Bruce Hershenson of West Plains, Miss., had spent 10 years selling vintage movie posters on eBay. Instead he now does that twice a week on his own site, eMoviePoster.com, using technology offered by AuctionAnything.com Inc.
"I talk to other people who have done what I did and they're happy with their decision. They've been able to get their business to the eBay business levels or beyond," Hershenson said.
His poster auctions on eBay had started at 99 cents each, so under the fee structure eBay imposed in January, he would have paid 15 cents to list each poster, down from 20 cents. But his average poster sold for $50, and eBay's take on that sale price would rise to about $3.07, from about $2.12 previously.
Even with a discount he could get by keeping his customer-feedback ratings high, he expected to pay eBay almost $20,000 more per year.
Sellers have also bristled at changes in eBay's feedback policy, one of the site's traditional hallmarks. In the spring, the company removed sellers' ability to leave negative or neutral feedback for buyers, though buyers can still offer negative assessments of sellers. EBay also adjusted its search engine so that items being hawked by people with poorer feedback ratings come up lower in search results.
Some sellers complain that this put them at the mercy of unscrupulous buyers who try to take advantage of the rating system.
"Many times you feel like they're really pushing it to see if you'll give them some kind of a refund," said Bill Cartmel, who sells records on eBay from Lewiston, Maine. "They'll float the suggestion that 'This isn't exactly what I expected."' EBay's Norrington said that sellers can report such abuse, and that the company hasn't seen it much.
Even with the rancor, some sellers clearly have benefited from eBay's changes. Steven Holt and his wife, Crystal, who sell DVDs from Denison, Iowa, say they've seen record sales since the spring, when eBay search results began favoring vendors who, like them, have high feedback ratings.
Yet Holt understands why some sellers may be upset. He notes that the uncertain effect of fee changes, combined with an iffy economy, "is naturally going to be a concern."
"When eBay makes these dramatic changes, it can make you very nervous," he said. "But again, eBay is doing what eBay believes it has to do to protect its marketplace."