I had some a-hole refer a company to me and I signed the company as a client. 3 months later, the referrer demanded I pay his finder fee of 15% of the contract for hooking me up with this client. There were other issues with this person too — including the fact that he was the human manifestation of slime.
Most freelancers and businesses have no problem paying a finder’s fee, but they need to up front — before anyone talks to the client — that you’re charging, how much, and for how long (1x, full contract, etc.) so they can adjust their price accordingly.