Duplicate Checker Function for Modzzz Premium RE Add Property Form

I need a custom checker function for the MODZZZ Premium Real Estate Mod's Add Property Form.  I also need installation instructions.

I would prefer to be able to customize which field or fields are used to check for duplicate entries.  If this is not possible, the duplicate checker must check to see if ALL (like a WHERE AND query not like an WHERE OR query) of the following fields are a match for any pre-existing record.  'state', 'city', address1, 'address2' (if not blank), and a field I created called 'my_membership_level'.

If a member tries to submit a duplicate property, the function will stop the form and display an error message such as, "This Property is already listed, please enter another property."