Detect if current visitor has already "liked" a webpage
I have a question regarding "liking" a web page outside of facebook.
I am familiar with placing a like button on an external web page -- I've done this for clients many times. However, I have a new client who wants a "Like" button, but also wants to know if the current visitor as already "liked" the page so he can display more content on his website. For example, for normal visitors, his web page displays 3 helpful hints. But if the user has "liked" the page, then the web page displays 10 more hints.
Thanks in advance for any help!