Hi,
I have purchased sketches and like stuff from 
Mandarake and like you didn't realize that they 
were copies. Now I have been told the copies are 
usually made for animators and other people 
involved in the animation process. These copies 
are used to help fix mistakes and such before 
finally putting the drawing on a cel. Mine did 
have red pencil marks from the head animator. 
Granted most of the copies are original and used 
in the process but I can understand your 
disappointment. Most sketches and such that have 
popped up lately from more recent anime are 
copies. Mandarake does try to list in the 
description that the item is a copy or at least 
not the original piece of paper. I don't know if 
this was the case with you. Your best bet is to 
contact them and explain your situation. Other 
than that I would just try to sell them and get 
some of your money back. Sorry I am not much 
help. Good luck and take care.

buttrflym