All items for sale on www.amazon.com have identifiers. There are four major kinds. The first two identify items regardless of whether or not they can be purchased:
ASIN—(Amazon Standard Item Number) An alphanumeric token that uniquely identifies items in the Amazon marketplace.
All items in the marketplace have an ASIN. This is, by far, the most common identifier.ASINs are used by the majority of ECS operations.
Listing ID—An alphanumeric token that uniquely identifies items in a Pro Merchant Seller's store, called a zShop, or a Merchant@'s store.
Listing IDs are much rarer. They are assigned to items sold by Pro Merchant Sellers who sell items in their own stores.
The second two identifiers identify items that can actually be purchased:
OfferListingId—An alphanumeric token that uniquely identifies items in the Amazon marketplace that can be purchased.
All items in the marketplace that can be purchased have an OfferListingId. This is, by far, the most common identifier for items that can be purchased.
ExchangeId—An alphanumeric token that uniquely identifies items for sale in a Pro Merchant Seller's zShop, or a Merchant@'s store that can be purchased.
ExchangeIds are much rarer than OfferListingIds because few items on www.amazonn.com are only available in a seller's store.