Let me address the warranty issue with a strange answer - it depends. It depends on what type of receiver you are buying and whether the warranty is from the original manufacturer. For example, Denon and Yamaha state that they will only do warranty work if the unit was purchased from an authorized retailer or e-tailer.
Here they are for Yamaha and Denon.
http://www.usa.denon.com/dealers/dealers.asp?l=1
http://www.yamaha.com/yec/customer/dealer.aspx
If you are not purchasing from an authorized e-tailer and you want a warranty, they will usually sell you a MAC warranty. My findings have been that by the time they add in that cost as well as shipping, you could have bought the item brand new in an unopened box. Which is the way that I like my electronics. Also, you may want to consider if you have to return the item that you will probably be responsible for shipping at least one way.
I would highly recommend that you check the web site of the manufacturer of the product that you are considering. Also, if you further break down the price to the hours of use you are going to get from a product that the difference really isn't all that much. Furthermore, I have found that peace of mind is worth a lot. I looked long and hard on eBay and around the web for a good deal on my 2500 and ended up bargaining with a local retail shop and got them to come down between 15 and 20%.
If you have any other specifics then let me know and I hoped I helped a little.