After a few days apart, eBay (NASDAQ:EBAY) is slowly working its way back as a client of Google's (NASDAQ:GOOG) paid search services. But let's not crank up Peaches & Herb's "Reunited" just yet.

The leading online auction marketplace learned a lot in Google's absence. An eBay spokesman told Business Week that traffic was actually higher in many of eBay's sites during the 10 days in which it reallocated its paid-search marketing dollars across Google rivals such as Yahoo! (NASDAQ:YHOO) and Microsoft's (NASDAQ:MSFT)

Sure, those days also happened to take place during the annual eBay Live event. A bump in traffic was likely, anyway. Still, it's got to sting when a company that was once Google's most prolific advertiser is encouraged by a temporary breakup.

"One of the biggest takeaways is that we are not as dependent on Google AdWords as some may have thought," eBay spokesman Hani Durzy told the magazine.

For a company like Google that is rarely wounded, words of that type can be steely daggers.

Anatomy of a breakup
The hot-cold relationship between the two companies took a turn for the lukewarm last year, when Google Checkout was introduced. The online-payment platform was a clear threat to eBay's own PayPal.

Google was naturally irked when eBay responded by banning Checkout as an acceptable payment source on successfully completed eBay auctions. eBay argued that Checkout was still unproven. OK, but it's a year later, and Google Checkout is still a no-no on eBay.

Popular retailers such as Aeropostale (NYSE:ARO), Sports Authority, and Linens 'n Things have no problem accepting Google Checkout, and we're to believe that it's not good enough for the homemaker in Toledo, Ohio, auctioning off her Webkinz collection?

Let's not beat around the bush here. Checkout is a threat to eBay because Google is committed to subsidizing its near-term losses. Checkout is not charging its merchants any credit card transaction fees until at least next year. It is also offering shipping discounts through a partnership with FedEx (NYSE:FDX).

It is wrong for eBay to restrict its paying auctioneers by limiting the ways that they can seal the deal, but Google's response proved infantile. On the eve of eBay Live, Google headed to Boston to steal some of eBay's thunder by preparing for a "Freedom Party" to vent to the media about its marketplace exclusion.

Google eventually withdrew its emotional response and canceled the eBay-bashing soiree, but the damage was done. eBay decided to take its contextual-marketing campaigns elsewhere.

Exposing Google
The world knows that Google isn't the source of the cheapest traffic. Second-tier search sites such as LookSmart (NASDAQ:LOOK) offer less competition for popular search terms. The current issue of Business 2.0 explains how arbitraging publishers are buying traffic from the cheaper to pages monetized through higher-priced Google ads.

This isn't the kind of stuff that will unseat Google from its paid-search throne, but it may lead some to wonder about the emperor's sense of fashion.

The unknown variable here is that we don't know the quality of the traffic that eBay was acquiring on the cheap. Increased traffic to is useless if auctions are less successful and close at lower bid prices. Until now, the saving grace at eBay has been that even though stateside listings have been sluggish, higher conversion rates and average selling prices have kept the growth coming. (Read more about that in my take on eBay's last quarter.) Spreading the wealth among several paid-search specialists would not be a smart diversification move if the ultimate traffic gains are weak.

Clearly, eBay doesn't think it will end that way. The 10-day test is too brief, but the current campaign reallocation will help flesh out an important third quarter at eBay. Right now, it seems as if eBay is the one calling all of the shots here. However, if playing the field proves unfulfilling this quarter, eBay will have little choice but to run back to Google with open arms and an even wider keyword list.

At that point, "Reunited' may not be the top choice of a Peaches & Herb song to score this rocky love story. I'm thinking something more upbeat, in the vein of "Shake Your Groove Thing."

Show 'em how to do it, now.

FedEx, eBay, and Yahoo! are Motley Fool Stock Advisor newsletter selections. Microsoft is a pick in the Inside Value research service. Read all of the original recommendation reports with a free 30-day trial subscription to either service.

Longtime Fool contributor Rick Munarriz is a satisfied eBay user, with 172 positive feedbacks to show for it. He does not own shares in any of the companies in this story. He is also a member of the Rule Breakers analytical team, seeking out the next great growth stock early in its defiance. The Fool has a disclosure policy.