From the link: http://www.alleywatch.com/2013/04/5-ways-to-spot-a-good-recruiter-in-the-rough/
1) Good recruiters are relationship oriented.
2) They don’t send mass, form emails. Ever.
3) You can ask them for references, and the feedback will be consistent and positive.
4) They have an actual mandate from a company or an actual relationship with the candidate.
5) Good recruiters could do their job if LinkedIn didn’t exist.