Partners told CRN that, like the companies cited by The Wall Street Journal, they had seen Software-as-a-Service vendors instructed by Walmart, as a condition of doing business, to port applications from AWS to Azure. Walmart is certainly not unique in making such demands, they said, which are rarely aired publicly.

But one well-publicized case in that vein, they said, was Home Depot directly working with Pivotal Software to introduce Pivotal Cloud Foundry to Google Cloud Platform. The home improvement retailer wanted to continue to use the popular development environment in the public cloud, but avoid giving business to Amazon's largest profit-generating division.

A Pivotal spokesperson told CRN that Home Depot, like other Fortune 500 retail customers using Pivotal Cloud Foundry for app development, prefer Google Cloud Platform or Microsoft Azure above AWS. Pivotal and Google "rapidly accelerated joint R&D efforts to add new capabilities," he said, "encouraged" by those retail giants.

At the same time, Pivotal and Microsoft have also stepped up efforts to integrate capabilities on Azure, "primarily driven by automakers," he said.

It seems car manufacturers prefer to avoid patronizing Google since they see the parent company, Alphabet, a competitor through its autonomous vehicle division.

Partners need to know about these industry biases, which can manifest themselves in a plethora of ways.

Webb said he's even seen one partner lose business with the U.S. Postal Service because the company sent a proposal by FedEx. He added that he knew a partner who was once left with the impression that a technology deal had been pushed aside by an Apple rival because an employee pulled out an iPhone during a pitch.

"Why would they spend money on someone who wants to put them out of business?" said a partner, who asked not to be named.

That partner said he's even heard of large financial services companies that tell their IT staff to use Azure over AWS because their mutual fund invests in Microsoft.

"Happens all the time," he said.