Trimming a horse's ears is somewhat controversial. Some people believe the ears should never be trimmed. Others will remove the hair from both the outside and inside of the ear. The traditional method, however, is to hold the horse's ear together and trim off only the untidy, excess hair. Trimming inside the ear removes the horse's protection from flies and can increase the risk of ear mites. A horse with trimmed ears should wear a fly hood when turned out. It's much easier not to trim inside the ear in the first place. Trimming only the excess looks just as neat.
1 Professional organizations and the U.S. Government Printing Office can also be indicators that a book is scholarly.  Book reviews can provide clues as to if a source is scholarly and highlight the intended audience.
In others, texts can continue to be considered valuable for longer. You should search for additional texts on the topic to find related sources, sources in which this source is cited, and sources that cite this source in order to get a stronger picture of its intellectual relevance and value. For whom is the source written? Is the intended audience a scholarly one? If so, it should have a clear bibliography that you will also be able to consult for further sources. Will you use the source as a primary or secondary text? If the material does not measure up to expected standards of scholarly work, it may still be of use to you.