I found the auction your talking about, if you look to the left in the photo he/she has another tank (also a dirty green colour) i assume that over stocked aswell.
Also only has a 1200 L / ph filter... that would only be good for up to 300 L maximum
So many people have no clue about fish keeping, imagine your tank, now imagine that in the ground and picture it as part of a stream - makes your tank look like a puddle when you compare it to a natural fish habitat doesn't it?