I don't know, but I suspect that they can. If I own some data, I should be able to give (or sell) it to you and not to someone else.

That said, once I've given it to you, if you choose to give it to someone else, I have no claim against that someone (although I might against you, depending on our contract). That's the heart of 3taps' position as I understand it; they get craigslist post data from third party sources like search engines, instead of scraping craigslist, and so do not have a contract with craigslist.