What you've got to do is buy a big domination dubloon coin such as a ten dubloon coin which last ti'me I checked cost about 14,000, then go to the golden dubloon,
you've got to be patient as many other people crowd it up, go to the first menu and buy something that only costs one dubloon then go to the eat section and eat the item.
You will then have all those leftover one dubloon coins to sell, and as one dubloon coins cost about 2500np or more, you'll make a hefty profit! Enjoy!