The difference being that those are local groups where you hopefully are not purchasing or selling a weapon to or from a group of people the United States Military is currently at war with (conducting kinetic operations, w/e) and has designated a terrorist group.
Yeah, its not hard to find places to buy guns on the internet.
It normally is fairly hard to find places to do so from terrorists or organized criminal groups overseas. Partially because, as you say, most of these you find quickly are honeypots, or scams, and finding ‘legit’ markets is not easy.