I was planning on smoothing pretty much all hard edges on this model with the bevel tool. But on quite a few of the edges the tool does not work, giving chaotic results as in the picture. I have tried resetting the scale and rotation of the object and I have removed all Ngons, it still gives this result. If anyone knows what's up or has a better alternative I'd be pleased to know. Thanks!
Looking at that screenshot, I think that the bevelled edges are crossing over each other. This is often caused when trying to bevel sharp edges that are in close proximity. You may have to manually delete the local geometry, use the knife tool ("K" in edit mode) to cut in new geometry and fill in the new faces.
I Fixed this edge in the end, I think what caused it was I didn't take proper care while extruding, accidentally extruding vertices over itself. I deleted the local geometry several times before but it didn't help. Paying close attention and with your tips I figured it was probably the extruding, so I paid a lot of attention this time and it worked. Now I just hope I can fix the entire model like this. Thanks!