A huge sign is when the grammar and spelling are horrible. Another sign is when the person continuously talks about how good the offer is...if you are telling me its the "Best Job Ever!" or "No Layoffs Here!", chances are its a scam. If the job is one that should require some degree of experience and yet the employer states that it will train, this is usually another sign.
Aside from those, I stay away from any job offer that is put out by an Employment Agency...as a general rule, the jobs that they have listed on job boards are only to draw you in...once you get there you are usually told that they don't actually have jobs paying as much as they stated in the description, and likely that they aren't even placing for that particular job anymore...I had this happen to me about 4 times before I stopped applying for them. This is not to say that Employment Agencies suck though...they are good if you go in knowing what to expect, and contact them for an appointment instead of the other way around...that is the only time I have had success with them anyways.
