well, most of the fan cels on YJ are completely 
original, not copied from a actual cel image, by 
the way almost all of the seller selling these 
cel does stat they are either doujin or 
reproduction cels, so I don`t see anything wrong 
with that.

so there is really no worry, if you can read 
Japanese, most biders are very careful, in 
general anytime there is a doubt, people should 
always ask the seller or post in one of the YJ 
forum.