Craigslist has no legitimacy in and of itself. It's simply a marketplace. Individual sellers in that marketplace may or may not be legit. You simply have to take reasonable precautions that you would take in any commercial transaction, when deciding whether, and how, to deal with a particular seller..
And apply the simple rule that if it sounds too good to be true....
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.