Context. The approach of developing software systems with the use of third partycomponents i.e. COTS or OSS has increased globally. In this study API product refers toeither a software component or a software service or both packaged together, that can beaccessed through an API. Developers are faced with plethora of alternative choices to selectan API product. With this increase in components adoption, API product providers are facedwith challenge of designing their product to be more attractive than others. This needs theproviders to be educated about the developer behavior when they choose an API product.Understanding the selection practices of developers can help providers to improve thepackaging of API products, making them more suitable for selection. Objectives. The objectives of this study is to investigate the criteria that developers usewhen reasoning about acceptability of a software component. Methods. A background study is performed to identify the evaluation criteria proposed inthe literature. An empirical study using Qualitative content analysis is performed. In the study the 480 reviews of different API products are analyzed to understand the criteria frompractitioners’ perspective. Results. 9 relevant criteria that developer use to reason about accepting or rejecting an APIProduct are identified. 30 sub criteria related to the 9 criteria are described in the study. Conclusions. This study concludes that the identified 9 criteria play an important role indeveloper assessment of the API product. It is also found that the criteria have significantimpact on the ratings of API product. These criteria could guide API product providers tomake better choices when developing the product.