I usually paint edges black. The idea is to allow the painting to be hung immediately without the necessity of a frame. Not that frames are bad but I believe the frame is what ties the painting to the room it’s in. So hang the painting for a few days or weeks then choose a frame.
This is a bit of a departure for me. Continue the painting over the edge and there may be even less need of a frame. It might still need a frame because it may look awful in a particular room. I thought painting the edge would be a royal pain but it wasn’t bad at all. Now this painting was very simple to do but even if it required some real work it still wouldn’t take long. My wife likes this kind of edge and she often has a better grasp of what looks good.
I have no idea if this would be more saleable. My daughter does this quite often and she sells quite a bit of work.