autobiogphnation is absolutely right and I didn't even think of that. My innokin mod had an authentication code, all my nautilus boxes do, and the box my ProVari came in does.
It is not unreasonable to expect a COA on a product you've invested a lot in, but not every high end mod has them, and as has been stated, if you're ordering online, make sure it's from either
1. The manufacturer's website/online store itself
2. A fully certified, acknowledged reseller, most manufacturers will list these on their website if said manufacturer has no online or physical storefront
2. A reputable dealer, whether B&M or online. A reputable enough dealer, even one that isn't a licensed reseller, should still treat you right and get you what you need. Also, I've heard some clones are actually really good, but then again, that's only SOME, which seems like it would be a dice roll everytime you buy a clone. You could come up big, or crash and burn on a device that COULD literally kill you if it isn't used/functioning properly
As far as getting ripped off goes, if it seems even remotely fishy, DON'T MAKE THE DEAL! You WILL most likely get ripped off. If that happens, consider it a learning experience and the money gone.
I'm sure every member on this forum could give you tales of getting ripped off in big ways. You may even already have a few yourself.
I went to a B&M that i thought was the only one in my town and got ripped off about $200. I should have asked for a refund immediateoy when the girl behind the counter couldn't even tell me which side of the battery to insert into the tube first.