Product Advertising API
Developer Guide (API Version 2013-08-01)

Availability Parameter Restrictions and Constraints

The Availability parameter carries with it a restriction and some constraints. The restriction is that the Availability parameter cannot be used with the Blended search index. When the Availability parameter is set to "Available", the only optional constraint that can be present is MerchantId=Amazon.

Parameter Description
MerchantId An optional parameter that can be used to filter search results and offer listings to only include items sold by Amazon. By default, the API will return items sold by various merchants including Amazon. The only valid optional value for MerchantId is "Amazon".