If an AFL club wants a player to do a preseason or a VFL club wants to sign a player they will get in contact with them manager or no manager.There will be players who miss out and then wont have a clue what to do after it. The managers will get them tryouts for rookie spots etc or maybe a vfl contract.
As for the pre-season training, I do know of player managers ringing AFL recruiting managers to "beg" for their clients to be given a preseason training invite. Something along the lines of "Can you do me a favour and have xx down for a couple of weeks training?".
Saving face when a player manager has signed a kid, pumped his tyres up and doesn't want egg on his face perhaps?