I didn't post the link at first, because I couldn't find it in my bookmarks, but I got lucky with my Google search:

    The people familiar with the negotiations said Twitter
    executives were shocked that they had not been given an 
    opportunity[1] to present a counteroffer. They said 
    Twitter was prepared to make higher offers [than $525M].

~ http://www.nytimes.com/2012/04/14/technology/instagram-found...