Assignment Contract

Hello to everyone that's reading this post:

Lets say I go to the a Real Estate Agent and ask them if I find a buyer for them will I recieve a finder's fee?, or Do I still have to make a Assignment contract over the contract that the real estate agent has from the seller to buyer?, or Do I just sign over the assignment contract to the buyer for my assignment fee?, or do I have to tell the real estate agent that I signed over my Assignment contract to someone else for my fee?, and if I'm missing some important information please do tell.

And also, Lets say I find a FSBO property and we agree to find a buyer for him/her do I fax a copy of the Purchace Agreement Contract to the seller to be filled out then He/She fax's it back to me and I hold on to it until I find a buyer then make a assignment contract then sign over both contracts over to the buyer for my fee and then walk away with cash in my pocket? if not what am I missing?

Thanks In Advance