Well, whether or not you actually allow cash withdrawals is of secondary importance. The fact is that these cards can be used as payments. It's money laundering if the authorities decide that it is, then it's up to you to prove that it isn't.

The best way forward for you would be to consult a lawyer from the place you're going to register your corporate entity in, and then the same thing with every place where you intend to do business with.

That's so you don't end up like mr. David Carruthers.

You're on the right track by looking at the ways in which the system can be abused. Things to watch out for: regular users (you're aiming for travellers, so a person that uses this year long should stand out), volume purchases (extraordinary amounts / numbers of cards) and so on.

Establish what you think are reasonable parameters and ruthlessly prune whatever lies outside that. (aka the paypal method).