I am referring to the “IsForSale” “IsPublicDomain” key. For sounds this is set to true when the user checks this box: (this was formerly the “Copylocked” button)
I agree this should be implemented in a less messy/confusing way.
This can be done in one GetProductInfo call, see Anaminus’ snippet above (only needs to be adjusted to filter out non-free assets as well with the same result from the GetProductInfo call).