"Contractor's fee" percentage in a fixed price remodel contract?

[Balazs Sipocz]

Hello, 

Is it normal to have a "contractor's fee" defined in % for a fixed-priced house remodel contract?

Additional Background

Contractor says there is a lot of "unknowns" in the project. When asked what happens if some parts of the work come it at a lower cost, he said that would be his profit and if it's higher, it would be his risk.

However, there is still a % at the estimate, labeled as "Contractor's Fee".

This is my first major remodel project with a GC, so I don't know what is standard. Is it normal to have a % markup as part of the fixed price contract?

Or is this some kind of trick because I don't know how it works?

There are in fact a lot of unknowns with the project, I just don't understand that if the items are already padded for his profit, why is there a % as well?

Is this common? Should I find someone else?