What is the deadline for participants to buy squares?

The cut off is generally the start time of the game.  The official deadline will be posted automatically in the Pool Notice.

Can the Pool Administrator buy squares on behalf of participants?

Yes, the Pool Admin does have the ability to buy squares on behalf of any pool participant, even after the deadline.

What happens if the grid doesn't get filled?

The randomly generated numbers will be displayed after the deadline.  How the prizes get divied up is at the discretion of the Pool Admin.

How can I tell who each user ID is?

Hold your cursor over a taken square to see who the User ID of the taken square corresponds to.

I've changed my mind and don't want a certain square.  How can I remove it?

Contact your pool administrator.  They have the ability to release squares so that other people can claim them.