Cash advances on cruise liner casinos was an interesting exception to this on some lines. (Also being phased out with a % fee added.) Each passenger on RCL used to be able to get $US10,000 each cash advance IIRC.
Take the cash to nearest bank on the daily stops, pay it into your card, and a couple effectively got 20,000 miles for nothing - plus any sign up or activity bonuses that might apply to your card. As long as you START the cruise with that sum pre-paid as a voluntary credit you are fine.
As I pointed out on another thread, (as it is my line of business) buying mint USA stamps from USPS on credit card and then taking them back for a cash refund OFTEN works too. (Trust me on that.

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A few $100 of course is no issue, (and not many miles for the effort) but for $20,000 or whatever there would be Managers quietly phoning the IRS I imagine.
Also as I pointed out in detail buying traveller cheques or Gold or Platinum bullion coins or bars etc on credit cards is also very likely to make you a profit if you are patient for a month or two and get lucky. It is
NOT guaranteed of course, as currency and bullion can go down as well as up, and you need to cover the skinny dealer margin first up, and the skinny sell spread.
Travelex for instance generally offers flyer miles on transactions, so you get miles for effectively buying cash. One guy here got a million or so Qantas miles and it cost him nothing and it was done in an hour.

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Glen ~
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[This message has been edited by ozstamps (edited 08-25-2003).]