That said, do your research before sending your work out. Good agents won't do anything like steal ideas from your ms, but there are fake agents out there. Check agentquery.com and Preditors & Editors ( http://pred-ed.com/ ) to see what the agents have sold, how long they've been around, and if there is anything shady about them. Also Google them!
I don't mean to make it sound like a scary world -- it's not! -- but your question just makes it seem like you're a little bit newer to the process, so I want to make sure you have the tools you need to feel comfortable. :)