One thing I would like to point out is that if a club really wants a player they would usually try to retain him before he comes off contract.
True but to re-sign a player you want the player also has to be interested in the contract. Perth may well have wanted to retain him but Bertos might have been more interested in returning to Wellington in the knowledge that he had a great chance of signing with the Phoenix. The guy probably has Phoenix posters all over his walls!