Craigslist is a great venue for selling bikes, but it's also the refuge of scammers, morons, and bored individuals.
Part of the problem is the anonymity provided by email. In your ad, you could request that all replies include the prospective buyer's phone number and that you won't respond to emails that don't include the phone number. Then just call them up rather than replying by email. When you get someone on the phone, it's much easier to tell if you've got an interested prospect, and you won't spend your time dickin' around with people that have nothing better to do than windowshop.
In the meantime, don't fret over it. Go about your business and consider how you might reword your listing to make it more effective.