Ben, a plausible explanation is that the person at Lugess is ordering the sets from Amazon using a stolen credit card. The consequence of your having received the package may be that Amazon would ban you. I have heard of this happening to someone who received items from LEGO Shop at Home that they ordered from a third party.
It seems to me that the only way for Lugess to be legit would be for them to have some kind of discount deal for merchants with Amazon. But I don’t see why Amazon would help other people undercut their own prices.