Third-party merchants selling goods on Amazon aren’t thrilled with recent fee hikes from the company that have been happening over the course of the past year or so. Nothing new there, but Reuters has an interesting report out today about how a growing number of sellers are exploring alternatives, including eBay, which has its own fair share of critics.

The report is gaining some attention in Amazon’s own seller forums. The reaction is a mix of criticism of the piece itself, some who think disgruntled sellers just aren’t doing their job well enough, and some agreement with various points made in the article.

Regardless, Amazon has raised fees, and cites rising costs (like those for fuel, for example) as the catalyst. While the report names other competitors like Walmart and eBay, author Alistair Barr suggests “Google may be the bigger threat” to Amazon, as it “already owns most of the necessary pieces, such as product search, listings and a payment service.”

“It began testing a same-day delivery service with retailers in recent weeks, sparking speculation it’s building a marketplace,” he notes. “A spokeswoman said Google is always working to improve the user experience, including shopping.”

Google, as you may know, recently switched to a pay-to-list model for Google Shopping, which is based on its product listing ads. So far, this seems to have been going quite well for Google, and for advertisers, as report after repot has come out talking up PLA performance. Soon, Bing, another Google rival, will also offer product listing ads.

Google and Amazon are direct competitors in a variety of areas, and a possible new service called Google Shopping Express could raise the stakes further. This is what Barr was referring to.

Google is also testing the B2B retail waters, don’t forget.