Some folks are under the impression that if they give other people information or opinions, those people will become significant competition. I know from many years of experience that you can tell people EXACTLY what to buy and how to make money and they still won't do it (whether lack of skill, lack of interest, the realization that it takes actual work, whatever.)
However, there's no need to insist that menoknow share his "secret" set with any of us. It's not really a secret, Lego sells it, the same information he's using is out there. Check Amazon and eBay prices, figure out what sets could be flipped for 20% profit (too small a margin for me personally to take the risk on a large number of sets, but I'm lamentably cautious), and you, too, will know the "secret" (and can come back and taunt me if you like, I don't mind. ) Let him have his fun thinking he's holding the keys to the kingdom.