Irony Can Be So Ironic: Is Ad Hominem Acceptable Here?

We have a rule here at the Playground with regards to comments -- no ad hominem attacks, that is, disagree with the argument, refute the purported fact, offer a counter-example, but don't attack the person. It is the argument, not the arguer that needs discussing. If Michael Moore suggests you lose weight, if Keith Richards tells you to stay away from heroin, if Rush Limbaugh tells you to be a good, caring, empathetic human being who doesn't lie, if Dick Cheney tells you to be careful with firearms, you ought to listen. It is good advice regardless of the source.

But are there times when the source does matter? Take this example from Anne, a Playground regular.

"My friend read a book titled Acing the Interview: How to Ask and Answer the Questions That Will Get You the Job. He noticed several spelling errors and typos and posted a review of the book to this effect. The author responded in a manner that makes me question whether he is qualified to right a book about professionalism.

Here's the review and the author's response:
By A reviewer
The advice itself in the book seems good, but when the first 13 pages have 6 typos in them it is hard to take the author seriously. This trend follows through the rest of the book and I would say on average I encountered 1 mistake every 3 pages or so. If reading a book with tons of typos, spelling errors and omitted words distracts you from the content, don't even bother with this book because it will drive you crazy.

dear "A"...this is the author...appreciate your thoughts and comments...sorry you were upset about the typos...HOEWEVER..you obviously aren't needing a job..if you were, you'd be more concerned about the content than typos....if you need the advise, you don't really care about the typos...and you aren't gonna count them..counting the typos won't put food on your table or cloth your kids..but, hey, send me the corrections and i'll pay you for your time..

Now, I don't want to interfere with anyone putting cloth on their children, but would poor editing and/or such unprofessional behavior give us good reason to think that the advice in the book was not the best way to ace an interview? sure, this goes in the "irony can be so ironic" file, but do we have good reason to discount the argument because of the arguer here?