is it the drywall is bad? if so that needs sanding and repainting - give a little more info what are wrong with the walls?
What exactly do you mean by bad walls? Do they have holes, uneven wall paper removed, wet spots, mold...indoors or outdoors?
Could you be more specific, maybe a picture?
If you paint a pattern or stencil on it you will camouflage some of the issues!
Hire a Pro!
What's the problem with the wall? The surface is uneven?