J-BusinessDirectory - How to avoid that all listings are shown in the search results?

When I click on the "RESET" button in the search filter, or when I just clicking on SEARCH without adding a ZIP or location before, then all listings are shown as a result.

How can i avoid this? Reasons:

1) Because of competitor reasons I dont want to show all listings that easy.
2) Later on, when there are a lot of entries, the list might become by far too long and shows irrelevant listings.

Thx

Hi, 

For the search, you can enforce the zip code to be mandatory. 

We consider displaying all listings as a search result a default. To have the search result filtered by a custom rule development is needed. We can provide you with a quote if interested.