My feelings on this issue are a little mixed. I can think of three distinct cases
1) You figure out the approximate method of a trick and you buy it so that you can learn more of the nuances and subtleties that make the trick work. This is what happens most of the time with me.
2) The trick could be something mathematical, in which case what sells the trick is your presentation. I would try and come up with my own distinct presentation for such a trick (instead of copying a performers presentation verbatim).
3) You figure out the method, and it turns out the method is based on elementary sleights/subtleties that are in multiple books you own. I do this very rarely, but if the sleights are already there in books I own and the guy selling the trick has nothing else to add, I might simply create my own version of the trick by referring to my books.
1) You figure out the approximate method of a trick and you buy it so that you can learn more of the nuances and subtleties that make the trick work. This is what happens most of the time with me.
2) The trick could be something mathematical, in which case what sells the trick is your presentation. I would try and come up with my own distinct presentation for such a trick (instead of copying a performers presentation verbatim).
3) You figure out the method, and it turns out the method is based on elementary sleights/subtleties that are in multiple books you own. I do this very rarely, but if the sleights are already there in books I own and the guy selling the trick has nothing else to add, I might simply create my own version of the trick by referring to my books.