The two major reasons for premature hair loss in brushes is constant use with out letting them dry completely and letting soap build up at the base of the knot. I would go the shaving brush wiki about brush cleaning and follow those instructions and see if that does not stop the shedding. Another cause of hair loss is abusive use such as excessive churning or pushing the brush against a bowl, scuttle or face. This actually causes the hair to weaken and break. I enjoy my Kent brushes and find them to be high quality brushes and have not experienced any hair loss. If you can, you may want to contact the original owner to see if he experienced the same condition. I expect that he did if you have just received the brush. Good luck.
<>< Sufficiently advanced incompetence is indistinguishable from malice. (Clarks law)