if they are from a local company and have a phone number they should be ok. a lot though if you respond will forward you to a website which is just a general resume pool type thing, I don t trust these. Even the legitimate job offers though are a long shot, because there are so many people looking for jobs. I ve responded to dozens of adds, and only ever heard back from a couple.
as with anything on the internet..... user beware! personally i wouldnt trust craigslist or any other site like that. for jobsearch i mainly stick with the regular sites jobsearch.gov, seek, mycareer.
Most of them are scams. Go check a real job board like Monster