Storytime: As a tween, I shoplifted (from a major outlet) a Rider-Waite tarot deck. From that day until the day, years later, that I gave the deck away, I never had an accurate reading with it nor a reading without very negative cards appearing (the 10 and 9 of Swords were especially "vocal"). Virtue prospers.
There are a lot of reasons why I think Damon Brand would be incapable of pulling-off a curse of this magnitude, a primary reason being his desire to cast it in the first place. If you are ready to communicate with your daemon, nothing in the universe is going to get in the way of that, much less someone's learnt, Protestant ideas about the sanctity of the profit margin. So, no, I do not think your work will be negatively effected by using the techniques in these books if you are using them with a sincere desire to evolve. No more than it would if you borrowed a book from the library.
However, if you do find any book genuinely useful, my guidance would be to buy a copy when you can. This is especially important when the author of a book is still alive.
Now, if you wanted to ask whether Brand's books are actually any good...