Many people do not understand the true meaning of proofreading services. They think that the readers who are in charge of the checking of the text, should follow its content and verify that the content is genuine and true. This is not correct at all. The readers must indeed read the whole text but not to check for errors in the content, but for spelling and grammar mistakes.
For example, if they are given a book about chemistry when they read it they will not concentrate on the correctness of the content, because they are not supposed to have previous chemistry education. They, however, should be very good at English (or whatever language the book is written in) so that they can recognize and correct any typos and incorrections in the spelling of the words.
Since offering proofreading services is considered a very important and responsible job it is very highly paid. This is so because the readers are liable for the correctness of the copy of the book which will be published. In other words they check the final version of it and make sure that the book meets all the grammar requirements of the certain country in which it will be issued.
Even though this is a very important job, there are many companies for proofreading that offer such services. Not only that, but they have many readers at the same time, that make a double or triple check of the book before it is given back to the publishing company. The idea of the double or triple check is that more incorrections are eliminated at the same time, since one reader is reading the book and another (or other two) follow the text which is read and correct any errors. Although this means that the proofreading company must pay for more employees at the same time, they still manage to earn enough money out of the services they offer, since this kind of secure check is very thorough.
Although all of this may seem as an easy thing to do, proofreading services are quite important because only the companies that offer them can assure that the book meets all the spelling and grammar requirements. That’s why author and publishers (especially!) should not be narrow-minded when it comes to this.