There are multiple ways to do this. First is by creating a variable like this:
Terms Count =Count([Terms Code]) in ([Sales #])
You have to add this variable to your report. It will display 1 for all Sales # 1000 and 2 for all Sales # 1001. You can apply a filter on Count > 1.
You can also do this using PREVIOUS() function as below:
Previous([Payment Terms Code]; ([Sales #];[Line #]))