I am just rather intrigued that some people 
don't
consider dougas/gengas as being cel related 
items

Well, the fact of the matter is that it has 
nothing to do with whether or not it is 
cel "related."  If it is a cel sale, what 
is "related" to cels has absolutely nothing to 
do with it.  A cel sale = a sale on cels.  Not a 
sale on cels "and all related items."  

Yes, sketches are precursors of cels.  But 
storyboards are precursors of sketches. And so 
are settei.  If you include that, what about the 
pencils the artist used?  They are precursors of 
the drawings.  The car the artist used to get to 
the studio?  That comes before the drawings as 
well.  Cel paint?  Cel books?  Frames?  You 
can't include something in a "cel" sale just 
because it is "related" to cels or because it 
happens to be shaped and weigh about the same as 
a cel.  

That's like going into the grocery store and 
seeing a sale on lollipops and then being 
annoyed that your bag of sugar wasn't included 
in the sale, since afterall, "sugar is a 
precursor of the lollipop."  <_<

Besides all that, it really is quite plainly 
stated on the page that douga are not included.  
I wouldn't call it fine print.  I use that font 
for the main text on my website o_o; lol.   It 
is stated right there (as opposed to the very 
bottom of the page or on some separate "Terms" 
page) and is not hard to see.

On Cels:
4) Cels are only $7 commission up to 10,000yen, 
$1 per 1000yen after. (*Cels do not include 
sketches, gengas, dougas, backgrounds, etc.)

Anyway, not trying to lecture (really I'm not!), 
just trying to explain so hopefully you won't 
get stuck in a similar error again.  Always read 
rather than assume.