Facilitate high value trade

I have a suggestion about high value trade.
Nowaday, decent gears worth far more than 2 billion zenny.
However, it is impossible to make a single character to carry that amount. It is pretty inconvenient.

Why don’t you make an item which can only be made from NPC By trading in zenny; let’s say 510 million? Then this item can be hand in to the same NPC for reward of 500 millions. Woora, now you can trade with this item at its face value of 500million which can be redeem at any moment. Multiple of this item can be stack. Now, you can trade at whatever crazy amount you satisfying with.

Sorry for my bad english.

Until dupes have been completely eradicated, zeny "tokens" are a no no.