Hmm. I'm still well enough to work in other fields so that I can finance my writing "habit".

I have to take exception to this:
Professional marketers will use the book as a currency. This ‘currency’ is used to a) get an email address or b) giveaway to gain credibility. Along with giving the book out, they gain customer contact information and begin customer relationships.
Building a relationship with the customer is the most important part. If a good book is given that adds value to a customer’s life, it’s likely that the customer will return interested in other products.
How will giving a book away give you credibility? The way I see it, giving your work away will just mark your out as a sucker who doesn't know the value of your own work.
It depends on who the customer is:
1. If your customer is a proof-reader, and you've paid their fee, then it makes sense to give them a copy of the (finished/published) book as thanks for their help, and to build good will.
2. If your customer is a publisher, they will not give two hoots if you give them a copy once the publishing process is under way.
3. If your customer is a bookshop, they will want as many copies as they think they can sell.
4. If your customer is an individual, and it's your first book, it may make sense to sell a book for a lesser price - but not for free. You, the author, also need to eat (as Rkcapps pointed out above).
That’s exactly how consumers think. If we receive something we like, that works for us, that adds value to our life – then we want to return to those products or that author/company for more
For example: You purchase a video game from Nintendo and enjoy it. You then are likely to return to Nintendo to purchase more games. Same goes from eating at a good restaurant, etc.
I'm sorry, but this is a false equivalence. He's comparing consumers who
receive something (gratis and for free) vs. consumers who
purchase something (from Nintendo or a restaurant).
I'm not sure if this is how consumers think. Personally, I evaluate each individual book on its own merits; if it the presentation is good; and if the content looks interesting or amusing, and is presented well.
If I've read the author's books before and enjoyed them, or if I know that the publisher is a good one (e.g. Thames & Hudson), that's a bonus, but it's not the sole selling criterion. The criteria I listed above are the most important to me. I'm just as likely to purchase a book from an author or publisher I've never heard of.
I've heard this argument before - and applied to artists, as well (e.g. on DeviantArt). "You should give your work away for free because it encourages other people to do business with you." Sorry, no. It only encourages people to take advantage of you. Don't sell yourself short. You worked damn hard on your book, you busted your chops doing research, and it's only fair that you should be paid.
By giving your work away for free or for low prices, you're not only hurting yourself but also other authors. Don't settle for less than a fair price for your books.
To come back to the Nintendo/restaurant example: you wouldn't ask a games programmer, a games artist, a chef, or a waiter - or a company manager, or the restaurant manager - to work for nothing. Why should authors be treated any differently?
Yes, I know I haven't sold my books etc... but that's just my take on it. As a consumer, I am prepared to pay a fair price to an author for a book. I don't expect anyone to give me freebies. If they want to (e.g. because I'm a friend etc.), then that's nice, and I'll ask them if and how I can repay the favour.

But if I see an author selling their books (e.g. in an event at a library etc.), then I do not and will not march over, bang on the table, and demand a free copy, as if I was an overindulged spoiled brat.

All right, rant over!

What do you think, hmm?