some classics I think are clearly into the black

1. doing a trade through a broker at $100/unit when the market was $98 yesterday.  Undoing the trade or doing an offsetting trade in private to make up the difference.  Move the print without it costing anything.

2.  Lying full stop re a trade.  This is the sort of thing the Enron types are doing time for (or at least paying fines).  More common than I'd like to think.

3.  offering through the bid in such size that the buyer cannot absorb it physically but insisting on all or nothing.  Easily done in barge lot markets.

4.  Refusing a buyer claiming credit issues etc where none really exist.  The brokers usually find a "sleeve" to bust this up.  IE put BP in the middle knowing both parties will trade with BP.

trying to remember the rest of the V..../MR playbook.

5.  Loudly offering through one specific broker all over the market (to force the price down) but not picking up any other phone to trade.  And hiding from the one broker until after the time of day the market prices are determined by Platts/Argus.  Pet brokers know where they make their money and will protect their best customers.

6. Selling early in the day before the bulk of the market is at their desks in order to set an artificially low price.  Then try to jawbone Platts into reflecting a low ball trade in the range.  Perhaps merely in the grey here.  Platts doesn't have to be stupid.  

7.  Not actually performing when the time comes.  Hard to prove damages if a small lot slips a few days, but the deal could have been done in a narrow date range to influence the print on Platts.  And perhaps paying damages on a small lot in order to make 10X on a larger one is a profitable scam.

8.  Agreements not to compete or to collude.  I've had major players suggest this to me over lunch.  "we can keep it off the phone lines".  no thanks.

9.  Bribe the reporter.  Perhaps just ugly rumors.  I've no proof whatsoever and no suspicions about anyone I ever worked with.

10. Threaten the reporter.  I've seen one shaking in her shoes at a party.  

If I wrack my brain I could probably think of a few more scams.  It's a little harder on exchanges.  The deals actually do get done, but even then players working in collusion can undo losing trades off exchange later.

but I agree with your basic thrust.  If I'm offering and there are no bids until I've moved the market 5%, tough rocks for the longs.  Buy my oil or STFU.

Good thing it's been 10+ years and my memory is so foggy.....