Because the question is different than the other topic, in my mind, I'll answer here:
I would not support a store that sells knock offs as their own (knowingly, myself knowing or the store knowing)
I feel this way because I know that designers and engineers work just as hard as anyone else. I think in some ways things get taken a bit far, like being unable to use VW logo's on a cafe press shirt design featuring a handpainted VW 1965 split window bus. In the case of such a blatant copy as the initiating case, no way, no how would I purchase that fabric and if the store involved was aware of the issue and left the fabric on the shelves, no way would I shop there.
There are always options, big box stores only have the power that the consumers give them.