A person I know -- I could call him client or business associate, depending on the project --, who has more seniority than I do, was approached by a big institution looking for a consultatn-programmer for a 6 months contract. He told them he knew a guy (me) who could very well do the job.
I was rather surprised when he told me that he'd negociate for me and keep a cut on my hourly rate, amounting to about 10%. Overall, he'd make more or less 5000$ with that deal.
I am all but comfortable with this and would rather give him a finder's fee, but I'm not really sure what would be a reasonable amount for it. Somewhere between 500 and 1000 would seem more than fair, but I'm open to other people's experiences and perspectives.
Keep in mind that it is reasonable to assume that even without him, I could have ended up in the candidates, since one of the recruitment agencies with which they deal have me in their database. Moreover, I recently worked for that same big institution through that agency, and had excellent evaluations.