Facebook today relaunched its classified Marketplace, intent on capturing the essence of the social-networking experience without ticking off millions of its users in the process.

It’s a big gamble for Facebook, which has been stung by criticism for earlier failed attempts to engage users in commercial initiatives. In 2007, Facebook tried to launch a service called Beacon, which gathered information about what users were buying on other Web sites. Users decried it as too intrusive; it came down after a couple weeks. Just two weeks ago, Facebook backpedaled after an unexpected backlash from users over an unannounced change to its terms of use, which appeared to give the site ownership over user content forever.

But immensely popular portals don’t live on love alone. Eventually, it has to monetize (beyond its current anemic display inventory and estimated $300 million in revenues). And, especially in light of its missteps, it needs a “win.”  

Enter the giant indexer-aggregator Oodle, which in December announced it had added Facebook to a long list of partnerships that include MySpace, Walmart and a deal cut a little over a week ago with AOL.

Oodle CEO Craig Donato gave us a sneak peek yesterday of what Facebook users will see today. For months, Donato has been touting the notion that the future of classifieds should be — or at least, could be — a more social experience. With the Marketplace relaunch, he’s proved it can be.

What Oodle has created, borrowing Facebook’s strengths, is a private-party classifieds channel that fosters a conversation about buying and selling things. In fact, when you post an item for sale, you’re asked why you’re selling it. That makes sense when you think about it. That’s exactly the sort of question a friend would ask you. It can be a pretty good conversation-starter that leads to a transaction.

The conversations become part of the listing on the listing’s own “wall” — something else that makes sense. Sellers don’t have to keep answering the same questions over and over again to prospective buyers.

The free listings are promoted through Facebook’s newsfeeds — the feature that tells users at a glance what their friends are up to. It looks just like another status message, i.e., “Joe is selling his laptop.” That’s about as unobtrusive as it gets.

It’s also as transparent as it gets. There’s no anonymity between buyer and seller. This isn’t user “1057894231@craigslist.org” trying to sell you a used computer, it’s your friend, Joe. Likewise, your friend Joe knows it’s you.

But if you’re browsing listings and don’t know Joe, his photo and a contact button is on the upper left side of the listing page. You’re a lot less likely to get scammed. 

“We wanted to create a place where people sell things, not a place where things are sold,” Donato told us.

There’s also a strong sense of social conscience in Facebook’s new social classifieds. You can buy and sell things, but you can also give things away, or give the proceeds of your sale to charity. And if your charity has a page on Facebook, the entire e-commerce transaction is handled by Network for Good, which handles online donations to more than 45,000 nonprofit organizations — and generates tax forms for the seller.

We’d have to say, there’s nothing quite like this out there. It’s engaging, different and elegantly executed by Oodle. It’s social.

As we said, listings are private-party only and free. For now, the focus is on “creating an engaging experience for users,” and not making money, Donato said. Wise, for now.

That said, money is being made in two areas: Oodle will run display ads on what it referred to as the “siderail” on the Marketplace link. Ads would reflect user searches. For instance, if a user was searching for an Acura, three of our ads might appear from local dealers with an inventory of Acuras in their metro area.

Additionally, sponsored listings will run at the bottom of search results.

It could be a killer app — if Facebookers don’t squash it first out of spite.

Somebody somewhere is knocking on wood.

We’ll have more in next week’s clients-only Classified Intelligence Report.

(Mya Frazier contributed to this post. Thanks, Mya.)