Applying to jobs requires plenty from you: time, energy, and (perhaps most important) savvy. You don't have time or energy to waste on questionable-seeming Craigslist posts and vague cold emails, and being judicious in your applications can save you a lot of extra effort. There are too many job scams out there, either looking to sign you on for a subpar (and often underpaid) position or even to steal your personal information. You have to be careful not to accept an offer that looks too good to be true, because it very likely is. Check out this flowchart from Resume.io—it details how to assess a job posting to make sure it's on the up-and-up, and also that it's with a company you actually want to work for.
This flowchart was created by Resume.io and used with permission. The original image can be found here.