How Twitter Cards Work (technical)

If Twitter could use common standard like microdata (proposed by w3c), it would probably be a better approach.

The big problem with Twitter product cards is the lack of real time information (ie the data shown to user is crawler dependent). So, e-commerce vendors with dynamic pricing needs (like hotels, airlines) wont use it much. E-Commerce vendors (like Etsy) where users are little less price sensitive have a better shot at using these cards.

This is a really straight forward explanation of how to implement cards in Twitter. Each social platform (Pinterest, FB, Goog Now, Twitter) requires a different implementation to achieve a similar goal. This is a good nuts and bolts view of what you need to do in Twitter to make it happen