As an example if you want to find the Quotes that have write in products set up your advanced find with Quote as the main record. In the search criteria select Quote Products (Quote) from the list (toward the bottom). Under that, select "Select Product"
as the field, "Equals" and the condition, and "Write In" as the value.
If you just wanted to find Quote Products that are write ins, make Quote product the main search entity and then select the "Select Product" again as the field.
Jason Lattimer