Does the author know what they’re writing about?
It is always a good idea to check who the authors of text books are. For example, if you are reading a book on TCP/IP by Douglas Comer, then you should find out who Douglas Comer is to see if he is a suitable person to write a book on this topic.
Why or why not?
Douglas Comer is a suitable person to write about TCP/IP, he is a professor of Computer Science at Purdue University and has written several books about TCP/IP and networking. He is a Fellow of the ACM (Association for Computer Machinery) and was also Vice President of Research for computer networking at Cisco Systems.