If you're building a suppression smart list, then alogn with the the filters to identify competitors, you can also include the "Not Filled Out Form <contact us>" filter in AND (also add the Web Page or Referrer constraint based on whether the page is a Marketo landing page or an external landing page).

This inactivity filter would exclude people who have filled out the Contact Us Form on that particular page to qualify for the suppression list even if they meet the other competitor criteria. You can use this smart list in the Member of Smart List not in <Suppression List> to get hold of people who aren't in the suppression list wherever required (e.g., sending out a marketing email). Just as an FYI, Marketo retains form fill data for 25 months from the date of activity, so competitors who filled out the form 25 months ago would still qualify for this suppression smart list.
Also, if you only want to apply the suppression criteria on people created via Form Fills/List Imports, then you should also include these as Source Type in the Person Was Created filter along with the Email Address contains <list of competitors domains>. If you have specific Download forms/List names you'd like to add, then use the corresponding Form Name/List Name constraint in the respective Person was Created Source Type filter.
