Bests & Worsts Reviews from Amazon

I bought this unit and was happy with how much dirt and dog hair it picked up. When vacuuming , I noticed a burning odor. When I was cleaning the bristle brush, I noticed that the end that fits into the motor was melted. I didn't have the original box so couldn't return it to Amazon, so I contacted Shark, who agreed to accept this item and send me a new unit. I received the new unit on Sunday and today opened the box and put the unit together. I did a test vacuum and after vacuuming a second room I noticed that burning smell again. I did clean the roller brush twice to remove the dog hair. I also had the setting to high pile since I was cleaning carpeting. I shut the vacuum off, popped out the roller brush to see that this roller brush is melted in the same spot as the first unit that was returned to Shark. It is now past the 30 days when I received the first order from Amazon so I can't return it. I called Shark and they can't accept a return for a refund since I bought it from Amazon, so all they can do is send me a new unit. There is a design flaw since the roller brush overheats and melts, so it wouldn't do any good for them to send this unit back for a replacement because that one would have the same issue. So I just spent $299.95 for a product that is defective with no way to return it for a refund.