Weren't Google (NASDAQ:GOOG) and eBay (NASDAQ:EBAY) the best of friends once? Google a few inane terms like "ox" or "pink dragon" or "dead cat," and you'll see eBay as a sponsored listing. That relationship has worked for both parties, giving eBay dirt-cheap leads from vague search-result pages.

The times, they are a-changing.

This week, eBay added Google Checkout to its list of payment services that are not allowed on the leading auction marketplace. Pull up eBay's Accepted Payments Policy page and click on "Some Examples" to see how Google's new online payment service has been blackballed on eBay.

Google and eBay both claim that Checkout and eBay's own PayPal are not competing services. Yeah, good one. According to eBay's terms, accepting Google Checkout as a currency of choice to seal the deal after an auction can be punished by having your PowerSeller status revoked, or having your account suspended altogether.

Threatened? You bet. Even if eBay plays it off as putting Checkout on the naughty list because it's too new of a payment platform -- and it is -- doesn't having PayPal embedded into the auction-listing process create a strong enough moat to show Google a little love?

For now, apparently not. And there's going to be a war here. The battle lines are being drawn. You have Google launching its new pay service. You have eBay hooking up in a strategic alliance with Google archrival Yahoo! (NASDAQ:YHOO). And you have Google Talk eventually butting heads with eBay's Skype.

There are too many collisions coming up in their future to make a friendship work. Get your pink dragons while you still can.

eBay has been a winning Motley Fool Stock Advisor newsletter recommendation over the years.

Longtime Fool contributor Rick Munarriz is a satisfied eBay user, with 167 positive feedbacks to show for it. He does not own shares in any of the companies mentioned in this story and he is a member of the Rule Breakers analytical team, seeking out the next great growth stock early in its defiance.