[SimplyUseless]

I think "Buy button" will not be forced to the retailers instead it will be an opt-in.

However think of these scenarios from the retailer's point of view:

1. Where Google button shows up on all links except my link, would it come under pressure and cave in; since all my competitors are selling by "Buy button".

2. Google may give priority to links who provide Buy button "integration". Pending anti-trust looming, this could put retailers under pressure as well.

3. Given an option to the end users to buy from Google vs. buy from another website, the end users could start seeing Google as a good brother.

Even though it could be an opt-in, it does not look like an opt-in when it comes to monopolies.

[TazeTSchnitzel]

It's brilliant, really. Impossible to compete with. Now customers have bought from your competitor without having to leave the results page. They won't even click on your site now.