We've seen this kicking around and just to make sure people are not falling for this scam we want to point it out. Apparently there is a link that scammers are posting that promises to enable you to change the quality of items in your backpack. Details are in a safe link here. As with anything, if something sounds too good to be true it usually is. Even if this were possible, once Valve found out, your account(s) would likely be banned and you would lose everything. And seeing as this isn't possible and the scammers are just pointing to a phishing program, if you were crazy enough to install it you would likely lose all your items or some trojan would be installed. Either way you lose.
Stay safe, don't download anything like this. Duping is over and these schemes aren't even worth attempting. If you want to make a profit at trading take the time to understand prices and earn it.
update: a few people have wrote to us and tried to equate duping with Valve replacing stolen items. While the result of both are indiscernible to anyone outside of Valve, it is not the same. Duping was the uncontrolled copying of hats via the old steam strading and in-game trading glitch. This is fixed. The other issue is when a player has a stolen/hacked account and items are replaced by Valve, effectively creating doubles if the offender is never caught. This has always existed and is a smaller scale issue. It is controlled by Valve and is not "duping". If this practice upsets you tell Valve about it.