diff --git a/src/alpine_bits_python/conversion_service.py b/src/alpine_bits_python/conversion_service.py
index 16a9258..6cad096 100644
--- a/src/alpine_bits_python/conversion_service.py
+++ b/src/alpine_bits_python/conversion_service.py
@@ -119,6 +119,28 @@ class ConversionService:
                 f"session must be AsyncSession or SessionMaker, got {type(session)}"
             )
 
+    @staticmethod
+    def _update_timestamp_if_modified(
+        obj: Conversion | ConversionRoom, session: AsyncSession
+    ) -> bool:
+        """Update the updated_at timestamp only if the object has been modified.
+
+        Uses SQLAlchemy's change tracking to determine if any scalar attributes
+        have changed. Only updates the timestamp if actual changes were detected.
+
+        Args:
+            obj: The ORM object to check and potentially update
+            session: The session managing this object
+
+        Returns:
+            True if the object was modified and timestamp was updated, False otherwise
+
+        """
+        if session.is_modified(obj, include_collections=False):
+            obj.updated_at = datetime.now()
+            return True
+        return False
+
     @staticmethod
     def _parse_required_int(value: str | None, field_name: str) -> int:
         """Parse an integer attribute that must be present."""
@@ -897,26 +919,39 @@ class ConversionService:
         existing_conversion = existing_result.scalar_one_or_none()
 
         if existing_conversion:
-            # Update existing conversion - only update reservation metadata and advertising data
+            # Update existing conversion using Pydantic validation
             # Guest info is stored in ConversionGuest table, not here
-            # Don't clear reservation/customer links (matching logic will update if needed)
-            existing_conversion.reservation_number = (
-                parsed_reservation.reservation_number
+            # Preserve reservation/customer links (matching logic will update if needed)
+            conversion_data = ConversionData(
+                hotel_id=hotel_id,
+                pms_reservation_id=pms_reservation_id,
+                guest_id=parsed_reservation.guest_id,
+                reservation_number=parsed_reservation.reservation_number,
+                reservation_date=parsed_reservation.reservation_date,
+                creation_time=parsed_reservation.creation_time,
+                reservation_type=parsed_reservation.reservation_type,
+                booking_channel=parsed_reservation.booking_channel,
+                advertising_medium=parsed_reservation.advertising_medium,
+                advertising_partner=parsed_reservation.advertising_partner,
+                advertising_campagne=parsed_reservation.advertising_campagne,
+                # Preserve existing values (managed separately)
+                created_at=existing_conversion.created_at,
+                reservation_id=existing_conversion.reservation_id,
+                customer_id=existing_conversion.customer_id,
+                directly_attributable=existing_conversion.directly_attributable,
+                guest_matched=existing_conversion.guest_matched,
             )
-            existing_conversion.reservation_date = parsed_reservation.reservation_date
-            existing_conversion.creation_time = parsed_reservation.creation_time
-            existing_conversion.reservation_type = parsed_reservation.reservation_type
-            existing_conversion.booking_channel = parsed_reservation.booking_channel
-            existing_conversion.advertising_medium = (
-                parsed_reservation.advertising_medium
+
+            # Apply validated data, excluding managed fields
+            validated_dict = conversion_data.model_dump(
+                exclude={'created_at', 'updated_at', 'reservation_id', 'customer_id',
+                         'directly_attributable', 'guest_matched'}
             )
-            existing_conversion.advertising_partner = (
-                parsed_reservation.advertising_partner
-            )
-            existing_conversion.advertising_campagne = (
-                parsed_reservation.advertising_campagne
-            )
-            existing_conversion.updated_at = datetime.now()
+            for key, value in validated_dict.items():
+                setattr(existing_conversion, key, value)
+
+            # Only update timestamp if something actually changed
+            self._update_timestamp_if_modified(existing_conversion, session)
             conversion = existing_conversion
             _LOGGER.debug(
                 "Updated conversion %s (pms_id=%s)",
@@ -998,7 +1033,8 @@ class ConversionService:
                     else None
                 )
                 existing_room_reservation.total_revenue = room_reservation.total_revenue
-                existing_room_reservation.updated_at = datetime.now()
+                # Only update timestamp if something actually changed
+                self._update_timestamp_if_modified(existing_room_reservation, session)
                 _LOGGER.debug(
                     "Updated room reservation %s (pms_id=%s, room=%s)",
                     existing_room_reservation.id,
@@ -1358,8 +1394,8 @@ class ConversionService:
             # ID-based matches are always directly attributable
             conversion.directly_attributable = True
             conversion.guest_matched = False
-
-            conversion.updated_at = datetime.now()
+            # Only update timestamp if something actually changed
+            self._update_timestamp_if_modified(conversion, session)
 
         # Update stats if provided
         if stats is not None:
@@ -1506,7 +1542,8 @@ class ConversionService:
         elif conversion.reservation_id is None:
             conversion.directly_attributable = False
 
-        conversion.updated_at = datetime.now()
+        # Only update timestamp if something actually changed
+        self._update_timestamp_if_modified(conversion, session)
 
         return matched_reservation, matched_customer