Shark (and Dirt Devil by the way) are companies that cater to big box stores. The manufacturer understands that the product going out the door in the big box stores won't be brought back there after a month or so( whatever that stores return policy is), as long as the machine lasts that long it is out of the stores hair, and then you're stuck calling a customer service line or hunting down a certified warranty service center in your area. The big box store made their money off of you so they are happy, and the manufacturer doesn't really have to stand behind the machine because Wally World is buying the product regardless.
Here's how you avoid this. Purchase from an independent dealer. They will know what machines hold up the best, and they can take care of you after wards since they are a dealer. The customer service will always be better because you can go right back to that same person who sold it to you if you have a problem, and for that reason they will want to sell you the best possible machine for the money. Since that is what they deal in, they will know what the best machines are in each price bracket.
Buy as much of the stuff you need off of independent specialty stores, because they will show you respect(you deserve it, you spent money there), because they value your business.