I believe it is totally up to the discretion of 
the seller whether or not to sell the cel with 
the sketch.....and I agree totally that it is 
heavily discouraged if the seller plans to 
separate the two to increase profit.  If you do 
decide to keep the sketch, maybe you could make 
note of the buyer's email address so in the 
future, if you ever decide to sell the sketch, 
you can contact them.  I'm sure the buyer would 
be glad to have the sketch along with the cel.  
My 2 cents! ^_^

Katie