Do not use type checking

app/models/lettings_log.rb

@@ -70,6 +70,14 @@ class LettingsLog < Log
     collection_start_year
   end
 
+  def lettings?
+    true
+  end
+
+  def sales?
+    false
+  end
+
   def form_name
     return unless startdate
 

app/models/log.rb

@@ -40,11 +40,11 @@ class Log < ApplicationRecord
   end
 
   def lettings?
-    is_a? LettingsLog
+    false
   end
 
   def sales?
-    is_a? SalesLog
+    false
   end
 
   def ethnic_refused?

app/models/sales_log.rb

@@ -38,6 +38,14 @@ class SalesLog < Log
   OPTIONAL_FIELDS = %w[saledate_check purchid monthly_charges_value_check old_persons_shared_ownership_value_check].freeze
   RETIREMENT_AGES = { "M" => 65, "F" => 60, "X" => 65 }.freeze
 
+  def lettings?
+    false
+  end
+
+  def sales?
+    true
+  end
+
   def startdate
     saledate
   end