Is there any way to make an uneven/distorted face even again?
Here is a screenshot demonstrating my problem.
How do i fix it?
This is only visible in render more, and not in edit mode.
The polygons with the undesirable “creases” do not have coplanar vertices.
How do I fix this?
Make sure all vertices in the polygon are in the same plane. There are a number of ways to do this, do an internet search.
EDIT: If you don’t really care that the surfaces are bent, switch to smooth shading in the Tools sidebar and the “crease” won’t be so visible, I think.
I noticed that these creases don’t show up when you render in cycles render.
Aren’t these bent/distorted faces called ngons?
I noticed that these creases don’t show up when you render in cycles render.
Hmm, I don’t see any difference between BI and Cycles renders as far as the visible crease is concerned. Instead, the controlling factor seems to be Flat or Smooth shading as I said.
“Ngon” is typically used to refer to a polygon with more than 4 vertices. Strictly speaking, triangles and quads are also ngons because they also have n vertices, but we already have specific names for them. Any polygon with more than three vertices can be “bent,” but of course a triangle can’t because three points define a plane. That, incidentally, is why renderers only render triangles 
You could try selecting individual polys and then it edit mode, choose Mesh->Clean Up->Make Planar Faces. However, if you want it to be one face instead of multiples, it may actually be quicker to just rebuild it.