I have never used Craigslist for chicks but I am going to be listing some soon.
I would just advise the 'buyer beware' aspect regarding breed and gender. If they swear they are all pullets I would be wary unless you know something about the breed (or cross) and can judge telltales for yourself. There are people out there who swear by some 'my granny taught me this' method for gender ID and they are about as accurate as swinging a sewing needle over a pregnant woman's hand to figure out the babies gender. Same goes for breed. Some places are reputable and you get exactly what they say you will. Some just want that one sale and will figure calling a black chick an Australorp is good enough even if there are no Australorp Roos in their pens and maybe two hens.
Just educate yourself and you should be ok. If in doubt about an add or such, check here. Someone may know someone who bought from them or at least be able to send up warning flags.