How do I prevent pilling?

It has nothing to do with the quality of a product. The reason for pilling: fine hairs get loose, rub against each other and form small balls.
 Consistent treatment with a special cashmere comb promises remedy. Use it to remove the loose hairs, wear the jumper and then wash it. Repeat the procedure two or three times. This should stop the annoying pilling and your favourite jumper will look like new again. I would advise against cashmere shavers. The danger of tearing holes into the knitting is too great.