Actions after a custom search that inherits from CRM_Contact_Form_Search_Custom_Base and that include WHERE clauses to filter is_deleted throw errors

It's because of validateUserSQL tripping over the substring "delete".

Suggest altering the substring search to look instead for the variations of the exclusion words that have white space before or after, i.e. fail on matching the regular expression /\sdelete/ OR /delete\s/

If you don't see a problem with that solution then you can assign back to me and I'll update.