You never know, sometimes people find outstanding deals. I got a mint Helm's Deep in late Feb for $60, is that believable? Of course there are drop shippers and plenty of other scams, but there are still plenty of legit methods to get some discounts, even on those sets that Lego Corporate doesn't want discounted.
I do think most folks are telling the truth, but it's a definite that there's some embellishment going on- it's human nature. I could say, "Back in December, I bought an Architecture Studio for $135 and sold it two hours later for $300. Easy $165 profit." Or, I could say "Back I December, I bought an AS for $135 and flipped it for $300. After sales tax, fees, and shipping, I had a net profit of $85." Both of these would be true, but that first example sounds a lot more impressive, doesn't it?