If you're doing the hiring, then what you're looking for in a 3rd-party recruiter is really one thing: can they provide qualified candidates to you without you

If you're doing the hiring, then what you're looking for in a 3rd-party recruiter is really one thing: can they provide qualified candidates to you without you needing to do much work or hand holding. They should be doing basic filtering for skill level, relevant skills and location. Preference is given to companies that can find people quickly, that can recruit diverse candidates, or that can do a good quality tech screen (Triplebyte)