I used to work for a carpet cleaning company and we used a carpet rake to keep the fibers going in one direction. You should be able to find one of these rakes at Home Depot or Lowes. That way your not trying to wrestle the vacuum going one direction.
The other option you might try is adding more light to the room. I understand that this isn't always possible but it really will help. Believe it or not it will actually help with traffic patterns in older carpet as well. If your carpet is starting to get worn out and you've had it cleaned but it still looks horrible just add a light. I would use a spot light to show customers. After the carpet is cleaned you still have a traffic pattern from worn fibers. The light does not bounce off of these fibers anymore. If you incorporate a bright light the pattern goes away. Then you know it cannot be cleaned any better. Anyway I digress.
The rake may be a better option. At least they will see the carpet all one direction as they walk in at first. It may get moved around with traffic but they will see nicely raked rooms to start and it will help the understanding that it is textured. Good luck!