I am not an expert, but I think that a buying keyword should be very specific - something you would search before you buy something.

Are you referring to the phrases by themselves or as an ending, eg:

kitchen appliances for home

kitchen appliances for the home

check whether you see any adwords campaigns for concrete keywords
if yes, it is one of flags that keyword is buying

thanks.

Yes, as in "Kitchen Appliances for Home", rather than "Kitchen Appliances Review"