I've made a suitelet that has a sublist of some transaction lines. The sublist has a column of checkboxes for the user to essentially approve or deny the line. I'm wanting to handle the checked lines one way, and the unchecked lines a different way when the user submits the suitelet. I'm struggling to understand how I can determined which lines were checked/unchecked after the user submits the form. Could anyone help with this?

How have you added the sublist to the form? In this scenario I usually value a longtext field with a JSON data before submitting the form and then read the value in the form submitted values. (POST parameter)