Welcome to the forum! I bought my VSX-23 from Best Buy back in 2009, and a couple of months later my buddy saved a lot of money buying a VSX-21 from a third party on Amazon. He was happy with the transaction, but it very well might not be the same company that you're looking at. I paid extra for piece of mind, but I haven't brought mine in for any warranty work.
Amazon offers some protection if you buy through them, but I'm not aware of that extending beyond 30 days (I haven't read their policy lately). My best advice is to read the feedback on the company that others have left, hopefully from a lot of reviews. If a product is sold by a third party but fulfilled by Amazon, then you know that Amazon has it in their warehouse and will ship it - so no chance that someone is just going to take your money.