I think you're right, it's poor selling skills to 
not identify which series are for cel.  I suspect 
most collectors collect only specific series, and 
personally, with multiple notices of sales these 
days, I really only look at ones I suspect will 
have cels I'm interested in.  (Not a lot of pure 
browsing time, I'm afraid!).  But on the other 
hand, it is sort of nice that it is sometimes 
clear that there is a fellow collector trying to 
thin out a collection rather that a rapicous 
investor, huh? :)