Maybe that was all the store had in the OP's favorite artist. Perhaps the person did not have enough time to purchase a new one online. I don't get the big deal over it being used. The store where I purchase stuff like that make sure they are in perfect condition (no scratches or anything) before they will sell them. I have found at least there it is not uncommon to not be able to find a new CD or DVD but to have several used available. It could easily have been that the store did not have the boxed set the OP asked for and this was the best they could do.
I just looked up that boxed set online and it was going for $40, so chances are even if she could find it, it was out of the suggested price range.