If a clified ad is posted in the Riverfront times, can I trust that it is reliable?

I have been looking for a way to get my foot in the door as an actress...I do not yet have the experience necessary to get an agent. I thought that doing "Extra" work would be a good place to start, and there are ads for Extra casting in my city in the Riverfront times. Naturally I am wary, because I have discovered many scam sites online. Can I trust these ads? Any help or advice would be greatly appreciated.