Sep 24, 2015 12:37 PM|Rion Williams|LINK
It depends on how you are actually wanting to output them.
Based on your previously provided logic, it looks like only the checkboxes that were actually selected are going to be stored within your Session, so you know that those will be checked. So as mentioned in your dilemma:
Dilemma: When a user clicks the back button after visiting the parts details page they have to, again, deselect the checkboxe(s) they want to exclude from the search results and hit the search button again to generate the desired results.
You would basically check for the Session value within your Page_Load event and iterate through your CheckBox list and check the values that were present in the Session :
if(Session["selection"] != null)
// Get your selected items
var selectedItems = Session["selection"] as List<string>;
foreach (ListItem listItem in Equipment_Fields.Items)
// Select this item if it is present
listItem.Selected = selectedItems.Contains(listItem.Value))