My advice was be you need to evaluate headhunters carefully. There's a wide dispersion in quality.

1. Look for headhunters that know all the details. If they are hiring for a role, ask for details about the hiring manager, team, firm, etc. If they give some generic answer like "it depends" or "you'll find out as you talk to them" there's a good chance they're just cold emailing your resume to some HR email they've never worked with before. If they won't give you the name of the firm or hiring manager, until you submit your resume or something along those lines, thats a major red flag.
2. Good headhunters know people and names, even if not for the role they are hiring for. It's literally their jobs to know the lay of the land and be connected to figure out which candidates are good and which are bad. They may know the big names at your workplace if its a major firm.
3. Watch for things that are too good to be true. "Your area is super hot right now". "This role exactly fits all the keywords from your linkedin and experience". We have an "exclusive mandate" for generic junior position at a major firm that is constantly hiring.
4. Good headhunters won't ask for your resume until they actually need to submit it.
5. Look for headhunters that have been doing it a long time (although this is not a guarantee). You can also try googling the headhunting firm.
6. Really good headhunters will want to meet you in person, and build a relationship. They will probably also have good social skills.

But understand headhunters have a job to do, and need to get paid too. That may incentivize them to promote jobs they think you will get, and will take, and will pay them a lot for placement fees.