AdWords advertisers can now insert order IDs into AdWords conversion tags so duplicate conversions from the same device are automatically filtered out.
Google quietly announced this news in a brief Google+ update this week, saying you'll be able to review more accurate conversation data by minimizing duplicate conversions, which will help you make better budget and bidding decisions.
"Until this update, advertisers added website code to make sure conversion tags didn’t fire again when people refreshed or returned to confirmation pages," the post says. "For example, if you’re a hotel brand, you may notice customers returning to their booking confirmation pages, perhaps to find the reservation number or room check-in time the day before a trip. By including an Order ID into conversion tags, AdWords will not count these subsequent conversions with the same Order ID, so they won’t show up in your reporting."
There's a support page available here if you have any trouble figuring out what to do.