Algae will be in every tank - this should not be a reason to not buy. But to properly clean will take time and elbow grease. This needs to considered when agreeing to a price.
It is a 90 gallons with 20 gallons sump and he want 300 $ for it but i just trade yesterday some stuff that I had for a 12 gallons nano cube and the cuestion is wich way I can go the 90 g or the 12 g with the 90 g im little scare about the algae