Unreported Scammer

I'm assuming the people you know were scammed quite long ago.
I remember after the new mobile authenticator thing, valve retracted the help they used to give people (i.e gave people their items back if they were scammed or hacked) (Forgot where I saw it, but so far this was what could find only: http://store.steampowered.com/news/19618/)

Also from the years I have traded, I have seen lots of scammers (like a fk lot) but only saw 2 or 3 that were trade banned. Valve rarely bans users unless the user's actions affect valve in a big way (like chargeback etc), so most scammers get spared.

Also did you double check the steam profile from the steamgifts page and the person who scammed you? There are alot of people who thought it was 1 guy scamming them, but in fact it was just an impersonator.
(Anyway I know of a guy who had 100+ rep on steamgifts and scammed a total of $3k or so worth of keys from 100s of people [he was selling mgsvphatom pain when it was coming out for 2keys lower than the next lowest market price at the point of time]; he is perma banned here now though, so even if it might appear to be a good guy, if a deal is too good to be true it probably is.)