This is the step that causes the most confusion. You must check (and un-check!) the correct boxes for the duplicate entries in order for the protection to work.
There are two types of rows now visible in your Step 3 table: Light Green and Red/Salmon. All of these rows need to be modified by you.
The Red/Salmon rows indicate a problem and you will not be able to submit your list without rectifying these.
1. The Light Green Rowyour user identries are the Dummies. These will have the Dummy entry name ("Bombay" in the example below) with your BGG user id name to the right.
Check the games that you want to trade for these duplicates. Your games appear as the first set of black columns at the top and bottom of the table (vertically). The duplicate entries ALSO appear as columns, to the right of your games (and also in light green). NOTE: The grid position which corresponds to both row & column of the duplicate entry is 'blank'. There is no way to 'check' that position in the grid. This is intentional.
2. The Red/Salmon Rowusername entries are the geek list entries that comprise the dummy entry. In the example there are three copies of Bombay, which together equal the single duplicate entry. These need to all be checked in the corresponding column for the dummy entries (the columns indicated in green to the right of your games).
You must DESELECT all of the grid positions where your games appear (the vertical columns in black).
These red rows are essentially defining the dummy entry.
Depending on how well you did, you might experience some problems. This first warning indicates that you've generated an entry for Duplicate Protection (the "bombay" entry below) but you aren't using it. That is, you haven't checked off any of the games you would like to trade for that entry.
To Fix: Check off one or more of the games you are trading (first set of columns in black text). Make sure you do not check any of the columns with a light green background.
The second possible warning indicates that you've generated an entry for Duplicate Protection but the entry contains no games.
To Fix: Check off the games that comprise the dummy entry. This means finding the games in the list that should be included in this dummy entry (highlighted in red/salmon) and check them off in the similarly named column (green column).
The third possible warning indicates you have checked a dummy item too many times. That is, the item which is one of the duplicate entries in your dummy item, is also checked by you as an item to trade.
To Fix: Find the row that is highlighted in red and make sure the dummy entry (vertical column in green text) is the only item checked.