I've reported this to CDPR :

In Floatsam after you save Dandelion and Zoltan ,if you pass the ark that is behind the market plaza,a group of bandit will attack you and one of them drops quest item that y can sell for 1 oren and rebuy at 0,this will virtually grant unlimited gold...

I've tried and i made 2000 g in 5 min...

It seems like a really boring way too make gold your better off selling crafting materials your not going too use.

If I ever get that far I will check it out. I need all the help I can get.

Cheers