Interesting to see if this is the start of a big change or a one off. There are so many sites selling links quite openly. I often use a backlink checker that is on page one of google if you search for that, and the main purpose of the site is clearly to sell backlinks.
One human spending just a week trawling through different sites could easily uncover hundreds of backlink selling sites and ban them. I've always wondered why G don't do that. The problem is that link selling is so prevalent that effectively Google have till now been sending a very mixed message.