The easiest way is to use parameters.
If you can attach the packaged workbook, the people in the community can help easier.
Please see if you can achieve using combined Sets
1. Create paramters for the two products : Prod1_param and Prod2_param
2. Then create sets on CustomerID with a condition :
MIN(Name of the Product Field) = Prod1_param
MIN(Name of the Product Field) = Prod2_param
3. Then combine the above sets and select "Shared Members in Both sets"
4. Bring the combined set to the rows shelf and CNTD(CustomerID) to text shelf
Hope this helps!