diff --git a/backend/auction/models.py b/backend/auction/models.py
index 79c9734..d9ea264 100644
--- a/backend/auction/models.py
+++ b/backend/auction/models.py
@@ -1,7 +1,7 @@
-from django.db import models
 from django.contrib.contenttypes.fields import GenericForeignKey
 from django.contrib.contenttypes.models import ContentType
 from django.core.exceptions import ValidationError
+from django.db import models
 
 from core.models import MainModel
 
@@ -36,11 +36,11 @@ class AuctionItem(MainModel):
     content_object = GenericForeignKey("content_type", "object_id")
 
     class Meta:
-        unique_together = ('auction_id', 'content_type', 'object_id')
+        unique_together = ("auction_id", "content_type", "object_id")
 
     def clean(self):
         # Restrict content_type to specific models
-        valid_models = ['vehicle', 'equipment', 'trailer']
+        valid_models = ["vehicle", "equipment", "trailer"]
         if self.content_type.model not in valid_models:
             raise ValidationError(f"ContentType must be one of {valid_models}")
 
diff --git a/backend/bid/models.py b/backend/bid/models.py
index f0edcbd..4b8b50b 100644
--- a/backend/bid/models.py
+++ b/backend/bid/models.py
@@ -21,7 +21,7 @@ class Bid(MainModel):
 
     def clean(self):
         # Restrict content_type to specific models
-        valid_models = ['vehicle', 'equipment', 'trailer']
+        valid_models = ["vehicle", "equipment", "trailer"]
         if self.content_type.model not in valid_models:
             raise ValidationError(f"ContentType must be one of {valid_models}")
 
diff --git a/backend/vehicle/models.py b/backend/vehicle/models.py
index 40a07dd..fcd248f 100644
--- a/backend/vehicle/models.py
+++ b/backend/vehicle/models.py
@@ -81,7 +81,7 @@ class UnitImage(MainModel):
 
     def clean(self):
         # Restrict content_type to specific models
-        valid_models = ['vehicle', 'equipment', 'trailer']
+        valid_models = ["vehicle", "equipment", "trailer"]
         if self.content_type.model not in valid_models:
             raise ValidationError(f"ContentType must be one of {valid_models}")
 
@@ -98,14 +98,14 @@ class SavedUnits(MainModel):
     content_object = GenericForeignKey("content_type", "object_id")
 
     class Meta:
-        unique_together = ('auction_id', 'bidder_id', 'object_id')
+        unique_together = ("auction_id", "bidder_id", "object_id")
 
     def clean(self):
         # Restrict content_type to specific models
-        valid_models = ['vehicle', 'equipment', 'trailer']
+        valid_models = ["vehicle", "equipment", "trailer"]
         if self.content_type.model not in valid_models:
             raise ValidationError(f"ContentType must be one of {valid_models}")
 
     def save(self, *args, **kwargs):
         self.clean()
-        super().save(*args, **kwargs)
\ No newline at end of file
+        super().save(*args, **kwargs)