In fact, it happened juz recently. There was this 
FY grp shot cel w matching BG tt was being sold 
but from the scan, it looked kinda dark and dull.( 
i love colors and vibrancy) Still it was a grp 
shot & tt's rare so i half-heartedly made an 
offer. The seller was a little reluctant but 
accepted it anyway. At that pt in time, if he 
rejected it, I would prob have shrugged my 
shoulders and look for other FY cels.
Then when it arrived and I opened the package, lo 
& behold, I was stunned. It sure looked different 
from the scan & not what I imagined.
The colors were brighter & richer...there was more 
contrast^_^ not to mention the 5 sketches that 
came w it, dougas & layout/concept drawings.
Now it's one of my faves, hope i never have to 
sell it :)
U can see it at the my gallery at the URL above.
Of course, there have been disappointing moments 
too but such things sort of make up for them.