Once, at an anime con, a well-known cel dealer 
offered me a special price on three cels I was 
interested in.  Only problem was, his "discounted 
price" was actually slightly higher than the 
total of the prices as marked. -_-

I don't think he was trying to rip me off... just 
lazy with math.  Can't say that it changed my 
outlook, other than it has motivated me to double-
check his totals everytime I buy from him (or 
from anyone else, for that matter).