The concept behind Craigslist is that the buyer and seller meet in person. The buyer gets to see the merchandise in person, the seller gets to see the money in person. Once both persons are satisfied that the transaction is what they expected, they do the deal and leave. It is harder for one of the parties to misrepresent their offer. Even if you question what the seller is representing in his ad, you don't provide payment until you see real evidence in person. If either party turns out to be not legit, then the other party is only out their time and perhaps travel effort.

This is not to say that the seller is legit, but it is different from how you would approach a deal on ebay for instance. If I was suspicious of a seller on either site, I would ask more questions hoping that the responses to the questions would provide evidence that the seller was legit or not legit. Then I would have to decide to go to the next level.