What to do in negotiations

[swamp]

I understand that it is none of my business but knowledge is power, and considering that this is an extension (therefore no work required to place me this time) I think that a reduction in rate is justifiable. Am I incorrect?

Knowledge is power, but a fat agency margin (in itself) is no justification for a rate rise. It could mean the agent would be prepared to give you a small rise out of their cut, and not unsettle the client, which would make things easier.

But at the end of the day 22% is not a massive margin, IMO, especially if the rate is quite low.

[badgerpig]

As others have said, the only option you've got really is cards on the table threaten to walk if you dont get an increase, from my experience most agents will stonewall you as soon as you ask for an uplift mid gig,
it depends on what your skills are really, if its a common skill set the agents will just let you walk and get someone else in to replace you but if your niche you have more leverage. Rates seem to be low everywhere at the moment, and there's a lot of people on the bench who will undercut you.

you do have a good point though, the agency arent doing an initial sift of applicants or any procurement activity whatsoever as your already in place, so by rights they should lower their cut.

Good luck