This sounds pretty much like Heist, whose plot summary suggests a whole lot of doubleplay going on:
David Mamet takes this story of thieves along many twists and turns,
some of which work and some of which don't. Gene Hackman plays the
brilliant leader of a gang (Delroy Lindo, Ricky Jay & Rebecca Pigeon
as Hackman's youngish wife), which pulls off complex heists for a
despicable fence (Danny DeVito). After stiffing the gang on a jewelry
robbery, DeVito forces the gang to go after a Swiss gold shipment and
to use his nephew (Sam Rockwell) in the crime. No one trusts anyone
and every step is shaded with the unexpected.
Near the end there is a scene where it is revealed that the railing of Gene Hackman's character's boat is made out of the melted and reformated gold (though that isn't the end of the story either, I think).