Already a major seller of e-commerce ads, Facebook (FB) - Get Reportis gradually becoming a big enabler of e-commerce transactions on its site and apps. Monday's launch of a marketplace for selling locally-available goods is just the latest in a string of moves meant to turn the social network into a place where people actively search for and browse goods, services and businesses they're interested in.

But Facebook's latest e-commerce foray isn't that much of a threat to Amazon (AMZN) - Get Report, and only a slight one for eBay (EBAY) - Get Report. Rather, its online classifieds leader Craigslist that has the most to be concerned about. And Alphabet's (GOOGL) - Get ReportGoogle, though not directly threatened, might want to keep an eye on Facebook's efforts due to their potential implications for ad-targeting.

Marketplaces, accessible through the Shopping icon within Facebook's apps (PC support will arrive "in the coming months"), lets Facebook users shop for goods listed by nearby users, either by browsing or searching. Facebook prominently displays a photo (when it's available) with each listing. The company is also betting the fact that a seller's real name and profile is attached to a listing will lead to a higher level of trust.

Taking on Craigslist is a tough challenge, given the online classifieds firm's near-monopoly position in the U.S. But Facebook's giant user base gives it an opening, as does dissatisfaction with Craigslist's stale interface and lack of internally-developed mobile apps (some third-party Craigslist apps exist, however).eBay previously owned a 25% stake in Craigslist, but sold it back to the company in 2015.

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Moreover, since Facebook isn't charging any listing fees, there's no harm in a Craigslist seller choosing to also sell on Facebook. In fact, many users have already been listing items for sale on both Craigslist and various Facebook groups.

With Facebook making Marketplaces available overseas -- the service is currently available in the U.S., U.K., Australia and New Zealand, with more markets to come later -- the service is a threat to eBay's Classifieds business, which has a strong European presence. eBay's Classifieds revenue rose 15% annually in the second quarter to $207 million, and accounted for 9% of the company's total revenue.s

On the other hand, eBay's core Marketplace business, which largely involves items located hundreds or thousands of miles away rather than in one's hometown, shouldn't feel much impact. The same holds for both Amazon's direct and third-party marketplace sales.

For Google, the risk from Marketplaces, as well as other Facebook shopping services, is that Facebook will get a better understanding of what its users are shopping for, and use it to deliver more targeted e-commerce ads. While Facebook has a ton of data on a user's interests, likes and demographic profile that it can rely on for targeting, it generally isn't as good as Google Search at understanding what a user is looking to buy at a particular moment.

Putting product listings on its site and apps helps change that equation. Targeted news feed ads based on a user's Marketplaces browsing are a possibility, as are search ads run against Marketplaces queries.

Here, it's worth noting Marketplaces follows the successful launch of Facebook''s Dynamic Product Ads, which let users browse through a carousel of product photos, as well as its Canvas Ads, which show full-screen photos and videos of promoted items when tapped. They also follow the launch of tools that let businesses create mobile storefronts on their Facebook pages, and allow users to pay for these listed items on Facebook's site or app, via saved payment card data.

Not every Facebook commerce effort becomes a smash hit. For example, while the company has tried to take on Yelp (YELP) - Get Reportby enabling local business searches and providing a directory for local establishments, Yelp is still dominant in the local reviews space. And from the looks of things, Facebook's efforts to connect users with local professional service providers haven't yet had a major impact on Angie's List (ANGI) - Get Report.

But Craigslist's mobile shortcomings and lingering trust issues arguably give Facebook a better chance of success in the online classifieds space. And though the service is free, there could be lucrative opportunities for Facebook's core ad business.