When submitting orders with the 'Post' flag, you are always the market maker.
Use the 'Post' flag when:
- You don't require your order to be filled instantly
- You don't want to pay any fees
To enable the 'Post' flag, click the 'gear' icon at the bottom of the screen. This will open the order customization dialog. At the top right of this dialog, you can find the 'Post' flag.