the 2^31 in binary means 2.147B in decimal. After inflation come in, more and more items can not be directly traded. This cause a lot of problems that will need GM to step in. (scam, labor to process...)
Why not make a RO bank? each char can deposit to its own account's bank, and ask bank to swap item and zeny?
If RO coder can careful prevent dupe / hack on the bank, then It will be awesome.