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Iranian president Hassan Rouhani gestures as he gives a press conference upon his arrival at Tehran's Mehrabad Airport, on September 28, 2013. - 

Friday, Secretary of State John Kerry met with his Iranian counterpart and other diplomats for high-stakes talks on Iran’s nuclear program. The U.S. and allies have raised the possibility of gradually eased sanctions if Iran agrees to new restrictions on its nuclear program. A deal is far from certain, but even if it happens, unwinding the sanctions would be complex, since they go back decades and have gotten more complicated over the years.

The Geneva talks focus on the big picture, but even a simple tourist in Iran can get a sense of the dizzying complexity of the many sanctions.

"We tell our clients, just carry cash. In Iran, it’s the exception, not the rule that you’ll be able to use any credit cards,” says Jean-Paul Tennant, CEO of travel company GeoEx.

His firm sends many American clients to Iran and he himself spent two weeks there recently. Those hoping to make purchases that exceed the pile of cash they bring face a tortuous journey. Tennant offers the example of an American trying to purchase a fine Persian rug with a credit card. Typically the credit card transaction will be routed through Dubai, which is where the carpet will have to be shipped from.

That’s just one small example of just how complicated sanctions can be. And it’s only an aspect of banking, to say nothing of rules about oil and frozen assets abroad.

"They’re just voluminous," says trade attorney David Levine, who works on these kinds of issues as a partner at McDermott Will & Emery. "To parse through every particular restriction or prohibition itself is very complicated and so removing those piece by piece, I think, raises some complexities."

Not all sanctions would be hard to relax or suspend. The international diplomats meeting in Geneva have discussed unfreezing up to $50 billion in Iranian assets overseas.

"It is relatively easy for the United States to unfreeze a negotiated amount of Iranian financial assets," explains Richard Sawaya, director of USA*Engage, a business group that generally opposes trade sanctions.

Other sanctions will be trickier, especially since they won’t be lifted across the board. Saying Iran can sell all the oil it wants is easy. But that’s not likely. More likely are complex rules of how much it can sell and to whom.

"If you do it partially, I think that’s going to be difficult," says Hossein Askari, an Iranian-born international business professor at George Washington University.

Askari and other Iran watchers are quick to add that as tough as sanction removal can be, putting them back in place is tougher still. Doing so involves banks and companies around the world, not to mention approval from governments. So negotiators better be sure Iran will hold up its part of the deal.

Follow Mark Garrison at @GarrisonMark