Just when you thought Amazon.com (NASDAQ:AMZN) couldn't get any more convenient than its one-click checkouts and subsidized deliveries, now it's willing to sell to you even if you have holes in your pockets.

Amazon is in the process of incorporating the Bill Me Later service into its site, though it's likely to miss the holiday-season rush. The timing isn't a concern, however, since Amazon is now a profitable e-tailer year-round.

Actually, more important than the implementation is that Amazon, being so impressed with Bill Me Later, is acquiring an undisclosed minority stake in the company.

As its name implies, Bill Me Later -- a competitor to eBay's (NASDAQ:EBAY) PayPal Pay Later -- gives online shoppers the option of paying for a product as much as six months after the puchase. If they are deemed a worthy credit risk, they won't need to nervously input sensitive credit card information into an online shopping-cart platform. That may seem like a silly fear, especially with the bulk of credit-card transactions still taking place at the bricks-and-mortar level, but Bill Me Later is now there for folks who are gun-shy about e-tail or simply find themselves juggling outgoing payments.

Hundreds of online storefronts already use Bill Me Later. Web-based sellers including Overstock.com (NASDAQ:OSTK), Bluefly (NASDAQ:BFLY), and Bidz.com (NASDAQ:BIDZ) -- as well as the online storefronts of real-world titans such as Wal-Mart (NYSE:WMT), Toys "R" Us, and Cabela's (NYSE:CAB) -- all offer Bill Me Later as a checkout option.

Bill Me Later didn't need Amazon on board to thrive. It was already one of Inc. magazine's fastest-growing companies. In fact, the company has been an easy sell ever since market researcher Jupitermedia found that Bill Me Later users tend to spend more online when presented with the convenience of delaying payments.

Still, that doesn't make Amazon's leap insignificant. Now that the leading e-tailer is on board, a smaller rival will have a harder time not matching Bill Me Later's level of convenience. So Bill Me Later is getting a client, an investor, and a validation stamp all from a single handshake.

Well done.

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Longtime Fool contributor Rick Munarriz thinks buyers can abuse the generosity of delayed-payment services to their own detriment. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. He does not own shares in any of the companies in this story. The Fool has a disclosure policy.