Honestly if the hackers are doing dupes and its easy for them to do, they can still easily dupe items worth 10k or so, in multiple stashes. It still results in an approx 370M zenny per stack of 30K items sold to NPC using overcharge. Now imagine they had a few number of items that they can dupe each time, there will still be a huge amount of zeny flowing in.
Basically you just made their job more tedious but the root problem isn't solved. If they can dupe- and it depends on how easily they do it, this won't solve the zenny flowing in, but only slows it down depending on how much effort the hacker's willing to put in. At the same time, legit players get affected quite badly by this move though.
If it is a short term measure while your team attempts to get the root of the problem and break the duping process, i completely support your move. However, please don't take too long, because its also a fight against player satisfaction while this is going on. In the end only the hacker wins if zenny becomes expensive, because he is more incentivized to dupe the cheap 10k items as i mentioned above, given that zenny becomes more valuable to players who lost a means to acquire them legitly while hackers basically still have their unlimited source (albeit at a lower tap rate).
I agree with BlackCROSS. It really is not the smartest move you guys have done. if youre really going with this, don't take too long to find the root of the problem. Camp, you and the team have left a lot of bad taste in our mouths and i know you're trying but this will actually make every new player unmotivated to play. I still don't think this is a good idea.