Ekk. This is really too complicated to explain in 
just one message. So here's the summary:

I don't keep all sketches. But when I do, I 
state "sketch not included." Meaning the sketch 
exists, but is just that: not included.

I always keep the buyer's information so that 
(if) I lose interest in the sketch, they have 
first dibs on it. 

I never display the sketch if I have no intention 
of selling it. It's a nasty trick. It really 
sucks that someone cheated you out of the sketch. 

BUT... I don't think a missing sketch will cause 
anyone to pass up a wish or dream cel. If someone 
is interested in the sketch, arrangements can be 
made. I price my cels MUCH lower when I'm keeping 
the sketch. 

I never sell my cels and sketches seperately. To 
this day, all sketches I kept have been reunited 
with their owners. 

Whew!  ^_^