diff --git a/clients_protocol/stores.py b/clients_protocol/stores.py
new file mode 100644
index 0000000..8371462
--- /dev/null
+++ b/clients_protocol/stores.py
@@ -0,0 +1,186 @@
+"""Data definitions for store clients."""
+
+from collections.abc import Iterator, Sequence
+from fin_defs import AssetAmount
+from frozendict import frozendict
+import abc
+import dataclasses
+import datetime
+import enum
+import logging
+
+from . import AbstractClient
+
+DEFAULT_MAX_RESULTS = 1
+
+URL = str
+
+@dataclasses.dataclass(frozen=True, order=True, slots=True)
+class SellerInfo:
+    name: str
+    url: str
+    address: str
+    country_alpha2: str
+    company_registration_number: int | None = None
+    phone_number: str | None = None
+    email_address: str | None = None
+    validated: bool | None = None
+    creation_date: datetime.date | None = None
+
+    def __post_init__(self):
+        assert self.name.strip() == self.name
+        assert self.name != ''
+        assert self.url.strip() == self.url
+        assert self.address.strip() == self.address
+        assert len(self.country_alpha2) == 2, 'Invalid ISO 3166-1 alpha-2 country code'
+
+
+class StoreOfferProperty(enum.Enum):
+    AUCTION = enum.auto()
+    SOLD_OUT = enum.auto()
+    DISCOUNT = enum.auto()
+
+
+@dataclasses.dataclass(frozen=True, order=True, slots=True)
+class StoreOffer:
+    title: str
+    description: str
+    listed_price: AssetAmount
+    source: str
+    image_sources: Sequence[str] = ()
+    seller: SellerInfo | None = None
+    date_published: datetime.datetime | None = None
+    date_updated: datetime.datetime | None = None
+    properties: frozenset[StoreOfferProperty] = dataclasses.field(
+        default_factory=frozenset,
+    )
+    metadata: frozendict[str, str] = dataclasses.field(default_factory=frozendict)
+    price_shipping_estimate: AssetAmount | None = None
+
+    def __post_init__(self):
+        assert self.title.strip() == self.title, self.title
+        # assert '\n' not in self.title, self.title
+        assert self.description is not None
+        assert self.source.strip() == self.source, self.source
+        assert None not in self.metadata
+        assert None not in self.image_sources
+        assert isinstance(self.metadata, frozendict), 'Metadata must be a frozendict'
+        assert isinstance(self.image_sources, tuple), 'image_sources must be a tuple'
+        assert (
+            isinstance(self.listed_price, AssetAmount) or self.listed_price is None
+        ), f'listed_price must be an AssetAmount, but was {self.listed_price}'
+        assert (
+            isinstance(self.price_shipping_estimate, AssetAmount)
+            or self.price_shipping_estimate is None
+        ), (
+            f'price_shipping_estimate must be an AssetAmount, but was {self.price_shipping_estimate}'
+        )
+
+    @property
+    def is_auction(self) -> bool:
+        return StoreOfferProperty.AUCTION in self.properties
+
+
+ALLOWED_CATEGORIES = {None, 'video-games'}
+ALLOWED_REGION_NAMES = frozenset({None, 'japan', 'pal', 'ntsc', 'english asian'})
+
+
+@dataclasses.dataclass(frozen=True, order=True, slots=True)
+class Product:
+    name: str
+    category: str
+    platform: str | None = None
+    edition: str | None = None
+    region: str | None = None
+
+    def __post_init__(self):
+        assert self.category in ALLOWED_CATEGORIES, f'Unknown category: {self.category}'
+        assert self.region in ALLOWED_REGION_NAMES, f'Unknown region: {self.region}'
+
+    @staticmethod
+    def videogame(name, **kwargs):
+        return Product(name, category='video-games', **kwargs)
+
+
+@dataclasses.dataclass(frozen=True)
+class ProductPrices:
+    """Reference prices for a specific product.
+
+    Fields:
+    - product: Product that this object describes prices for.
+    - loose: Price for the product itself without any packaging.
+    - complete: Price for the product with all of its packaging and in-box extracts.
+    - new: Price of an unopened sealed product, with all of its packaging and in-box extracts.
+    - graded: Price of an unopened sealed product that have been graded by a professional.
+    - source: URL indicating the source of the pricing information.
+    """
+
+    product: Product
+    loose: AssetAmount
+    complete: AssetAmount
+    new: AssetAmount
+    graded: AssetAmount
+    source: str
+
+
+class ItemSaleStatus(enum.Enum):
+    SOLD = enum.auto()
+
+
+class OfferNoLongerAvailableError(Exception):
+    pass
+
+
+class StoreOfferAccessClient(AbstractClient, abc.ABC):
+    """Client for accessing specific store offers on specific websites."""
+
+    @abc.abstractmethod
+    def supports_url(self, url: URL) -> bool:
+        """Check if this client supports the given URL.
+
+        This method determines whether the provided URL is supported by this
+        client.
+
+        Args:
+            url: The URL to check for support.
+
+        Returns:
+            True if the URL is supported, False otherwise.
+
+        Performance:
+            Lightweight. Implementations should not send any HTTP requests.
+        """
+
+    @abc.abstractmethod
+    def get_store_offer(self, url: URL) -> StoreOffer:
+        """Downloads the description of the store offer."""
+
+
+class StoreOfferSearchClient(AbstractClient, abc.ABC):
+    """Client for searching for store offers on specific websites."""
+
+    @abc.abstractmethod
+    def search_for_games(
+        self,
+        max_results: int = DEFAULT_MAX_RESULTS,
+    ) -> Iterator[StoreOffer]:
+        """Searches for all games offers on the respective website."""
+
+    @abc.abstractmethod
+    def search_for_product(
+        self,
+        search_term: str,
+        max_results: int = DEFAULT_MAX_RESULTS,
+    ) -> Iterator[StoreOffer]:
+        """Searches for the given named product."""
+
+
+class ReferencePriceClient(AbstractClient, abc.ABC):
+    """Client for accessing reference prices for specific products."""
+
+    @abc.abstractmethod
+    def get_prices(
+        self,
+        product: Product,
+    ) -> ProductPrices | None:
+        """Gets reference prices for the given product."""