Failure of paint to dry to a smooth film, resulting in unsightly brush and roller marks after the paint dries.
Use of lower quality paint
Application of additional paint to "touch up" partially dried painted areas.
Re-brushing or re-rolling partially dried painted areas.
Use of the wrong type of roller cover or poor quality brush.
Use top quality latex paints, which are generally formulated with ingredients that enhance paint flow. Brush and roller marks thus tend to "flow out" and form a smooth film. When using a roller, be sure to use a cover with the recommended nap length for the type of paint being used. Use of a high quality brush is important; a poor brush can result in bad flow and leveling with any paint.