Here's a cool trick from the Final Fantasy VII Ultimate Guide By
Versus Books: If you have a rapid-fire
controller, and just want some free GP, put the O button on auto fire (if
it doesn't have this setting, put it on rapid fire and wrap a rubber band
around your controller or something to hold it down). Then turn Cloud around
so he's facing the Arm Wrestling machine, and put something heavy on the
D-pad so he'll keep facing that way. He'll keep playing the game, and you'll
rack up a couple hundred GP per hour you leave it that way.