Yep, Amazon isn't always the seller for items purchased through Amazon, so you would need to pay attention when buying items from them. If Amazon is the seller, the listing will say "sold by and shipped from Amazon" or something like that. Otherwise, you are buying from a third-party vendor that sells through Amazon. Just something to be aware of.

Bear in mind, of course, that I'm not a fan of the third-party sellers via Amazon arrangement. Unknown sellers (that would otherwise sell via eBay, and may sell in both locations) count on the buyer not realizing that Amazon isn't the retailer that they are buying from. So you can easily stumble upon dishonest sellers via Amazon.