It should be possible to set a default for custom fields including the check box field type.
For example and in particular, we have a customer field of "Assign public IP address" when using Hosting Controller integration. This is a checkbox and the default is UNCHECKED.
Ideally we could set the default in the product for this field to be CHECKED or UNCHECKED.
In this case we would have this set to CHECKED by default because everyone ordering a VPS is going to want a public IP address and the field is required by the integration or it won't assign a public IP address.