"Group buying"? I don't think I'd call a bunch of individual customers a "group" just because they visited the same site on the same day. I also don't think I'd call the site a "group" because the site didn't buy anything, they just arranged a deal for the individual customers.

"Group buying" would be people coming together as a "group" and buying a LOT of 1 thing, then splitting it up.

If we're going to call Groupon "Group buying", every newspaper in the US (and possibly the world) has been doing it for decades.