Fraying sound like the sort of wear that is sometimes evident along the edge of an area rug. I have never heard of that occuring with OP carpet cleaning. What does get discussed from time to time is what is called fuzzing or tip blooming. This can be caused by moving the machine too slowly over an area, or by there not being enough moisture in the pad, or by using a pad and glider that is too aggressive for the particular carpet you are working on. I have been using OP machines to clean carpet for about a dozen years, and have never had a customer tell me that I have left their carpet looking damaged in any way. BUT - in order for you to have the same track record - you should know that some pads, and some gliders, are more aggressive than others. Pads made of 100% cotton terrycloth are the most aggressive. Pads mad entirely, or mostly of synthetic fibers, are the least aggressive. For example, some people will switch from an all-cotton pad and and aggressive (holey) glider to a Tuway "ThinOne" pad, and a thicker glider if they think they might be beginning to see some fuzzing or tip blooming. The Challenger "Turbo" pad is also one with a high synthetic fiber content, and might also be used in this situation.
I have been using Enduro pads from Challenger I think they are 20% poly and 80% cotton. I have been using them on just about everything Berber cut nylon and CGD with good success. I also do not use a glider keep the machine moving and you should never have any problems