Standalone Addon
By itself, LibMerchant acts as an information collector for merchant items. Each time you open a merchant window, it will scan each item to check whether it exists in its library before storing the vendor sell price of the item. This price, when available, will be displayed in the item tooltip.
Library Mode
The addon will also contain an API that can be used by other addons to determine when the data from merchant windows becomes available for them to use. It will act as an entire replacement for the standard "Merchant*" functions since it will already have all of the information from vendor windows. This may come in a future release
Functions
LibStub:GetLibrary("LibMerchant-1.0"):RegisterCallback(<Name_of_addon>, <Callback_Function>) - Runs your function when all merchant data becomes available
Status
Planning and chat box spamming (debugging)