Just sent him a message
"Hi, i'm not surprised the oscar has damage, for 4 oscars i wouldnt use anything less than a 5-6 ft tank, at least 600 litres, you need to sell off these fish seperately as that tank will hardly take 1 adult oscar, 4 oscars in there is just cruel! "
Some poor person with no experience will buy this
(although if he paid $330 for it new hes dreaming if he thinks he will get $250, tank is way under filtered for 4 oscars)
and then wonder why the fish are dying or killing each other.
Feel like complaining to Trade Me.