Writing books is a whole process that goes through various proofreading but still, after so much proofreading there might be some mistakes in grammar or spelling but jimdorey book is free from all spelling mistakes and grammatical mistakes. So, the answer is "YES" may authors do mistakes in their books because we all are humans.

I suggest to all students please don't go for these writing services they are just reducing your excellence and making you a dumb student if you want to succeed in your life then write your essays and assignment on your own just as I did in my student life when I was a student of an online academy at https://icsoc.info/recognition/courses-platzi.php I only write my assignments my friends asked me to write and complete their assignments but I did not accept them because I don't want to make them lazy.