It is definitely not a production sketch. I've 
seen hundreds of authentic dougas/gengas, and I 
can fairly surely say that it is not real. This 
particular piece shows some of the tell tale 
signs of a reproduction:

1. line quality - the lines on this sketch are 
way too thick and irregular to be production 
artwork. Anyone who has studied any kind of 
technical drawing (and I mean anything from 
architectural to animation) knows that there is a 
proper way to draw the line - use a VERY sharp 
tip, apply even pressure while drawing, and 
rotate the pencil while drawing to produce an 
even-thickness line. (Believe me, I know - I've 
had plently of technical drawing classes over the 
years.) 

People who have seen authentic douga know that 
the line clarity is supposed to be very crisp - 
even width (fairly thin) and no 'sketchy' breaks. 
The drawing on ebay doesn't have either of these 
attributes.

2. color - when a douga/genga actually does have 
color to it, it is nearly always done very 
lightly. After all, it is the douga which is used 
to transfer the *lines* to the acetate cel; not 
a 'colored in' area - that's what the paint is 
for! Any drawing with as much and *as dark* of 
coloring as the drawing on ebay would produce a 
screwed up cel (when placed through the 
xerographic machine). 

Another problem with the coloring is the fact 
that is is darker in some places than in others. 
If you look closely, you will see areas that 
appear darker than others; you can also see areas 
where the coloring goes 'outside the lines'. No 
studio artist would be so careless as to make 
these mistakes (if they did, they wouldn't have 
been hired as clean-up artists).

Sorry, but it is not real.