I see you're already writing 'Click on domain name to buy' in a pretty obvious 'popup' that only goes away when you click on it. It's not really a tooltip. The popup should go away after a little while I think.
People have a habit of waving the mouse in the general area of where they are looking even though they don't specifically intend to click. How about when you hover, a cute little animated hand comes out of the smiley face and shows an inviting placard that says 'click me to buy'. That would fit right in with the style I think.
Personally I think this site is perfectly... - oh well you didn't ask what I thought of the site so let's leave that...