I don't see anything on the results page that would be filtering based on the select list on the search page. What did you do to try to set up the results to filter? The select name is "Search2", so at some point you would have to update the Database Search server behavior on the results page and tell it to filter a column based on the value of that select list.
Currently you have filters based on form fields "Manufacturer" and "NeworUsed", but I don't see those fields on the search page at all. For some reason your search settings are out of sync with your search form and need to be updated.