Adjust your vacuum cleaner to the proper height setting to insure that the beater bar or brush just lightly touches your carpet surface.
Shag pile carpet with long pile yarns tend to wrap around the rotating brushes causing damage to the yarn. For these products we recommend a suction-only vacuum or a vacuum cleaner with an adjustable heigth of the brush lifted away from the carpet so it does not agitate the pile.
Choose a vacuum cleaner with large wheels for easy maneuverability. Smaller wheels tend to loosen threads, while large wheels easily roll over longer threads and leaving no marks or dents.
Avoid vacuums with super-concentrated suction. They are suitable for low pile carpets and hard surfaces but not for thicker, high pile carpets.