My kitchen walls were painted a deep, cranberry red by the previous homeowner.

I actually like the color, though the paint job is bad in spots. When we painted the adjacent living areas the soft yellow color that you see in the pic, I thought I could clean up the edges where the colors meet. What you see is actually an improvement, but it still looks bad.
I haven't had good results with masking or painters' tape, though I'm willing to try it again, but usually I can freehand a fairly straight edge with a good brush (what you see here was done with a roller. How would a pro painter get a clean edge here???