Just reacting to your personal rule which I follow also: "Never buy a cel from an anime you 
haven't seen". Although I know I've bent the rule once or twice when buying a cel of a series I 
knew I was going to watch soon. That usually will happen if I've read the manga and am 
waiting to get my hands on the DVD or VHS. I've never really come across a cel that was so 
nice that I'd buy it without seeing the video.