Well,
I see a lot of different opinions about this issue, and on reality they are all "PLAUSIBLE" however, lets take a step back and think of this.
Some how, an international sale has come through when the site wasn't set up for such, someone paid $1,000 in items and paid what the shipping charges requested so, the Buyer done nothing wrong.
How would I deal with the issue (do it all the time...!), I would send a message/email to the Buyer, thanking him/her for the order and explaining that the shipping charges showing on you site, are only for national sales and that you weren't aware that International sales/order could be possible.
I would provide the shipping cost of at least 2 options, all with some sort of registration or tracking and advise that, the order can not be fulfilled unless the correct shipping charges are paid. I would give 48 hours to have that payment adjustment coming through but, I would be the one to send him/her (make reference of that) an extra invoice/money request, if that payment is not made, then the full amount paid, would be returned and the order, cancelled.
Yes, you tend to get a little harsh, as a seller, when someone rips-you-off and you want to put all these restrictions and securities however, if you are targetted to be ripped-off, on the other end, "they" respond depending upon the level of difficulty you present them with and the chances are, they will have a solution for each one and you will get ripped-off, like it or not...!
I had once an "honest thief"
, that told me that, he looks around the stores for those with rude messages about who they want their buyers to be and put all these warning messages, tags, whistles and bells about being "bullet proof", these guys love that, and that's exactly what they are looking for to "hit" as hard as they can, they pleasure is to target those people and show them that, the more red flags they wave, the more bulls they attract...!
I have had a huge difference in scam attempts, since I removed all the red flags and made it as discrete and possible.
Again, this has been working for me, it doesn't mean that it will work for you however, the chances are, the same rules apply...!
Cheers
George