If I take a 12 pound, 5" iron sphere and sell it for scrap, it's worth (depending on the going rate) probably somewhere between $1 and $5. Throw at in with a bunch of other scrap iron and it can easily be transported between state and international boundaries without raising an eyebrow.
If I put it on a little wooden base so it doesn't roll, call it a, "cannon ball paper weight," and put it on a gift shop on Gettysburg, I can probably sell it for $30-40.
If I can provide an authentic appearing document that states this same iron ball was a cannon ball recovered from the Gettysburg battlefield, I'm now looking at somewhere around $200.
If I provide convincing paper(s) verifying this is the cannonball that removed General Sickles' leg at the Battle of Gettysburg that very same, pedestrian iron ball would easily fetch six figures at auction.
The trick is in the provenance, and the matching documentation need not be authentic, but only appear convincingly so. The item and the documentation giving it value are easily transported/shipped separately and then matched up after clearing customs, audits etc.
Some billionaire buys a crappy abstract painting for $500,000. Everyone calls him crazy.
Years later, he donates the painting to a museum. An arts appraiser and the museum agree the painting is now worth $20 million.
So the billionaire spent $500,000 for a $20,000,000 tax deduction. Seems he wasn't crazy, but orchestrated a tax dodge.
Who knows if the painting is really worth anything? There's much fraud in art appraising.