Actually the best deals are found on this site; the problem with your friend is ignorance, not ARFCOM.
If he researched the deals he was finding it would be fairly easy to see whats a ripoff. A little guidance from his friends who have the knowledge, like you, who can say "look at these manufactures to be safe" and then cross reference prices using google and the manufacturers website like BCM, Spikes, DD should get him in the right direction. Also remember while yo think these prices are high, this is a flea market more or less. Posted prices are all negotiable. Make an offer and see what sticks. I'm reminded of the guy that has his used Nightforce listed for MSRP when its available new for $200 less from a number of online sources, and all that was needed was an IM/email saying "hey, you've got this listed for X, but I see in new here and here for Y, so I'm offering you Z". Sometimes they'll say yeah, ok, and counter. Other times its some guy that got ripped off and payed to much to begin with and is trying to find a sucker. Takes all kinds I guess, but its the same all over not just ARFCOM. Being informed and researching is the key to any purchase, as well as negotiation.