A guy has asked me to perform a song he wrote. I told him that I would be the co-writer and could include it as one of my recordings. He denied that part, saying he is the sole writer... if I wanted to include it as my recording, I must pay the fees to Harry Fox for the mechanical rights. He said he would promote the song and I would get performing rights for my recording.
So, if he is acting as publisher (correct or not?), he would get money for publishing, air play and tv related rights, and writing, and I would receive a minimal amount for the recording, IF someone purchased my actual recording.
Am I interpreting this correctly, or is it worth if for an artist to perform a song written by someone else that they are willing to promote , AND are there hidden costs involved that I my have to pay? If a songwriter requests that you perform their song, do I have to pay any fees for doing that or must I make sure I have it in writing from them that I do not have to pay a fee to record, sell, or perform it in public?

Just to be clear...you are asking for co-author credit for a song you did not write?