What to do when a role is advertised by many agents?

[DodgyAgent]

Find out who the client is and go direct.

Failing that, find out who the preferred supplier agencies are and go to them.

Or just apply to all of them and let them fight it out to see who takes the smallest margin.

If I was a contractor that is almost precisely what I would do (please dont tell anyone), but I would be smarter. If the direct route was not on I would pick one agency and make them think that I have several routes to the job and that they are the lucky ones to represent me. You need to convince the agency that you are the "man" for the job and that you meet all the criteria - not difficult just flatter them (without patronising them) Also keep feeding them information even if it is false. So when you call them, instead of "chasing" say that you have been approached by another agency..
Information is power