Cel-ers who set their starting bid at a penny 
with no reserve and then, once you've won it 
(thanks to DAYS of perseverance, dedication, and 
a high speed cable internet connection), inform 
you that they couldn't possibly sell it to you 
for a price that low and they are going to keep 
it unless you cough up X amount more!

But yeah, overexposed cels are a big one too.  
I'm so tired of those Meryl cels on YJ! that I'm 
thinking of buying them just so my hopes will 
stop getting high everytime I see cels on the 
Trigun page.  (I'd sell my own mother for a good 
Wolfwood! ;) )