I have (what I think) is a very good policy on buying BNIB items off of eBay, CL, (or in this case) Kijiji. I ask to see a receipt for the item before completing the transaction. Any reputable reseller of Apple products (Target, Best Buy, Apple, etc) will print the serial number of the iPad on the receipt. Also, don't be afraid to ask to open it to verify the contents and make sure the iPads serial (both in the software and on the back case) match the box and receipt. If they don't and it was sealed or sold as BNIB, be wary because it might be a used or even hot iPad that was repackaged. Also check and make sure Activation Lock isn't activated.
If the seller won't let you open the box, walk away from the deal immediately. This should send up multiple red flags as any good seller should allow you to open it and verify the contents before purchasing it. Also meet in a public place, like a Target, or Starbucks where people are always around just in case.
When it comes to buying these things off of, say, eBay, I'm usually a little less worried since the transaction is recorded. On classifieds, it isn't. You don't get a receipt or an order confirmation. Of course, be careful and good luck!