WordPress has massive support, that's true. However, out of the box regarding classifieds you really have to pull a lot mods to get what Osclass has out of the box. And then, for everything you need another plugin, since WP is virtually blank slate out of the box. Yes, there are tons of them (and many that you see, are not really free, because advanced features are payed - and for any pro service you need them), but there are compatibility issues sometimes, so you need more time to waste what works with what and so on. And, security related, many of those critical plugins are often hacked and exposed (granted, they eventually get updated, if not abandoned). As in every software, maintenance is the huge part of the deal, whether you'll hire someone, or rely on 3rd parties, that's up to you. I'm not saying WP is a bad idea, just that it has inverted counterpoints when compared to Osclass in many areas. Also, in Osclass you can really do some mods easy with functions etc. In WP not always you can pull it that way, solutions feel 'hacky' at best.