I have had mostly good experiences with Ebay, but 
about a year ago my car died and I decided that 
was it, I had to get a new car.  To pay for the 
down payment, I sold more than half my cel 
collection, including a beautiful TV Hotohori 
headshot *still misses the cel*.  It was bad 
enough to make the decision to part with so many 
of my cels - I have pretty much always been one 
to go for quality vs quantity, and so when 
someone chose "buy it now" for $350 I at least 
felt relieved- that's a lot of money to me and I 
needed money badly.  
Later I found out the person had been involved in 
shill bidding and other shady practices - after 
several weeks she did finally pay up but it was 
very upsetting.
On the other hand, I tried to buy some dvds last 
month, and sent payment the same day the auction 
ended via paypal.  2 weeks went by and I e-mailed 
the seller, who was charging like $10 for 
shipping- and they said, oh yeah, it was returned 
to us- we'll send it again.  Interesting- that 
address has worked for 50 other items to be sent 
to me, no problem.  Another week went by and I 
said "screw it" and demanded my money back.  Here 
the seller was actually very good, and refunded 
my money within a couple of days.
Happily, I ordered the dvds from a different 
seller, and got them in 3 days.  :D

Also- for the ebay sellers- I usually try and 
work out payment plans if the people will at 
least reply back to me if I don't need the money 
ASAP, and if you do need money ASAP and the 
winning bidder doesn't get back with you, try e-
mailing the next highest bidder- they are usually 
very happy to have a chance to buy the item, and 
often the bid is only about a dollar or so 
lower.