If it's a geometric pattern - the odds are high that the designer was "inspired" by someone else's work.
My "criteria/conscience" is sort of guided by "how familiar is this pattern? " "How hard did I have to work to figure it out?"
If it is mostly "familiar" blocks - there are all sorts of books available on how to mix and match them. Then my guilt level is low.
If it is something like intricate paper piecing, then I would probably just buy the pattern - if I could easily find it.
However, if the pattern is out of print or not available, my guilt level is close to zero.
I have often wondered how much royalty money Jane A. Stickle's descendants/relatives got from the Dear Jane book and spin-offs. - or donated to the museum. (As far as I know, none!)
So how many current quilting/pattern books have been based on quilts already made?