I was informed that at a staffing company they rate you after you leave an assignment, is this true?

Answer 1

True with the staffing companies I've worked with in the past.

Answer 2

On the time slip the co you work at usually has a space to show any comments, and to check "satisfactory' or "Unsatisfactory" and that's about as far as it usually goes.
However, if your performance is terrible they will usually call the staffing agency and tell them they don't want you back.

Answer 3

Probably. But in some ways, you get "rated" at any job you're at. Plus, if you're a great employee the higher the rating, the better for you.