Ya i would be extremely cautions using craigslist. If anything why would they be using craigslist and not a reputable site like dice or monster? Either they are doing shady stuff OR they are cheap and don't want to pay the registration fee. Either way i would stay away.
I used Dice, Monster, Career Builder, Robert Half and would hitup the local companies I would apply to directly (IE in my area Cerner, DST, SAIC, ect).
Ive also found that recruiters are used a lot in IT. At first (before i was in IT) i was always weary of them but after a while realized it's just how most businesses hire IT now adays, especially small to mid sized companies that don't have a specific HR recruitment department.