Great, so /r/gundeals, which was nothing more than a sales aggregator for law-abiding online retailers, is gone, but /r/the_donald, a vile, rampantly bigoted, conspiracy-theory-peddling shithole, is allowed to stay?
[1] https://www.reddit.com/r/DarkNetMarketsNoobs/comments/8641hg...
[0] there were products that aren't legal in certain states or cities, but nothing that is illegal at the fed level.
Those that did sell guns were federally licensed retailers, gundeals did not (to my knowledge) allow for private sellers to post. All federally licensed (FFL) retailers must perform a background check (or transfer to another FFL to perform one) before transferring to a purchaser. I don't see how any of that could be considered as not "law-abiding".
All of that applies only to the US of course, but I'm not aware of other countries having deals there.