Hi,
A page is defined by the current menu item in joomla. So you can assign a module to some pages and not others only if those pages are on different menu items.
For the checkout, by default you stay on the listing menu item where you came from. So you can restrict a module to the listing and not the checkout.
However, if you set the "force a menu on checkout" option of the configuration, your checkout will potentially be on a different menu item than your listing. That way, using the "menu assignment" option of your module, you will be able to have it on your listings but not on your checkout.
For a more fine grained display of modules based on the current page, you can use the extension Advanced Modules Manager.