For that site, it would be a combination of the community http://www.deals2buy.com/sdeal.htm, and also the editors of the site finding deals.
Notice that most of the deals are affiliate links. Sometimes they and the vendor have partnership where if they the vendor offers a discount, deals2buy will post an affiliate link (but just because it's an affiliate link, doesn't mean that's the case).
In Canada, red flag deals is one of the top 10 sites in canada. http://www.redflagdeals.com/forums/ . Go under the Hot Deals FORUM...and it's community. Go under the DEALS tab on top, and that's the site editors (And some of those are the same posted by the community).