I think jOe nailed it; it's not a real good job. Whoever did it should have cut the plugs from wood that more closely matched those areas of the stock, and then made sure it ran the same direction. Then it could be blended with staining, false graining, etc. if necessary. The fit is poor; that's why the lines are so distinct. In my days in the music business I've seen totally invisible repairs done to fine stringed instruments, but you gotta know what you're doing. I'd find a guy who does, and have him do it right.
