If you want to prevent importing multiples, the easiest method is the following:
1. Check the "Unique" option for the field that identifies your records from one another. This can be something like a product ID, or an e-mail address. Here's more about the "Unique option.
2. While doing your upload, there will be an import policy step that asks you if you want to "renew" or "create new". If you click "renew", Ragic will check if the key field exists (usually the first column of your import file), and ignore the ones that are already there.