trust your gut. they're sales people, not technical people, so judge them by the appropriate metrics. i.e.:

are they putting you in front of the right companies? are they asking you questions about your needs? are they pitching you on the job (it should be worthy of a pitch), as well as vice versa? are they working with the right hiring budget?

these are the basic questions you use to judge the quality of a sales person. they have to "get it" on a relationship level, not a technical level.