Step 1 - Get an account and withdraw everything from bank, make sure you have say 5 to 20million for maximum effectiveness
Step 2 - use your 5 - 20mill, and open 20 - 30 auction windows (search for items that costed 5 to 20mill), and BID BID BID on every items, (Note: you only have 30 seconds, before you can no longer bid)
Step 3- after 30 seconds, you NP at hand will become negative! I achieved -200,000,000 , and managed to dupe a good 100m each time i did this, and bid on many HT weapons and r99 stamps
Step 4- after auction processed, you will have your 200m+ worth of items and with negative -200mill NP , you can send the items away to a storage account, and ice the account with -200m+ NP
1) have several accounts, dont involve your main account
2) side account have 5 - 20mill,
3) use items that are HTS to do the bidding, if you bid 20mill on a junk item, thats too obvious isn't it?
And, have fun duping!