if you check the top websites in each country, you will always find that among the list are several classified ads websites.
In the USA: ebay.com, craigslist, autotrader, etsy, backpage, recycler, oodle, ebayclassifieds, olX, letgo, walllapop
In mexico: segundamano, vivanuncios, ebay, mercadolibe.
In Poland: gumtree.pl , olx.pl, ebay
in Belgium: 2ememain, 2dehands, kapaza, ebay.be
So basically whether if i am a local buyer or a global buyer, it is kind of annoying to go through each one of these sites.
(The same way it was annoying to check every airline before expedia, or any job board before indeed).
In the last few years investments in online classified ads has been booming so much that ebay has began investing in its own network : http://www.ebayclassifieds.com/m/ClassifiedsNetwork