Here's a tip for when there are a bunch of cels 
by the same seller: all the skin colors are the 
same.  Kenshin does not get colored the same as 
Larva, who is not the same color as Asuka, who is 
certainly not the same color as Beldandy.  As a 
fancel artist, I can certainly tell you that not 
matching up the fleshtones properly is a really 
big temptation because its so goddamned hard to 
do sometimes.  Flesh is flesh, right?  But 
generally, guys are a lot darker than girls, and 
girls like Beldandly are a lot lighter than girls 
like Asuka, and I'm not even going to get into 
the underlying fleshtones each of 'em has.

Another tip... IT SAYS ITS A FANCEL!  WAH!  I'm 
sorry, but I have a cel that SAYS its a fancel in 
the title, many times in the description, the 
picture has 'cels by gwenb' written across it, 
and generally mention stuff about the materials I 
use to make sure I get high quality stuff, and 
someone buys it and then say 'what, it was a 
fancel?  Oh, I'm sorry, I don't like fancels' I 
want to beat them over the head.  Especially if 
it was an original painting that doesn't appear 
anywhere in the series, because I can sometimes 
believe that they didn't notice the little smudge 
that is my signature in reproduction cels...

*cof*  sorry.  People who don't bother reading 
the description or title of what they're buying 
piss me off.  But I will admit that some people 
try to mislead you with fancels, by only 
mentioning a tricky word like 'hand painted 
reproduction cel' once in the description, 
or 'artist reproduced' etc.  So read things 
carefully.

Of course, there's the people that don't say 
something is fan done at all, but I think picking 
those out already got covered.